Allah (SWT) says in the Quran - Humanity had once been one community ˹of believers before they lost faith˺. Then Allah raised prophets as deliverers of good news and as warner, and revealed to them the Scriptures in truth to judge among people regarding their disputes. And no one disputed the Scriptures except the very people who received them after clear proofs had come to them—out of jealousy. Then Allah, by His grace, has guided the believers to the truth regarding those disputes. And Allah guides whoever He wills to the Straight Path. (Surah Baqarah, 2 : 213)
When ignorant people attempt to trace the history of 'religion' they tend to the view that man began his life in the darkness of polytheism and that in the course of time, corresponding to man's progress, this darkness gradually receded and light increased till man arrived at monotheism.
The Qur'anic version, however, proclaims that man began his life in full light of the Truth. Allah (SWT) revealed this Truth to the very first man He created (i.e., Adam (as)), one to whom He intimated the right way of life for man. Thereafter the human race remained on the Right Way for some time and lived as one community. Later, however, people invented deviating ways. This did not happen because Truth had not been communicated to them. The cause was rather that some people willfully sought to acquire privileges, benefits and advantages beyond their legitimate limits, and thus subjected others to injustices. It was in order to enable people to overcome this corruption that Allah (SWT) sent His Prophets. These Prophets were not sent to found separate religions in their own names and bring new religious communities into existence. Rather the purpose of the Prophets was to illuminate before people the Truth which they had allowed to be lost, and once again make them into one community. As mentioned in the Quran,
لَقَدْ أَرْسَلْنَا رُسُلَنَا بِٱلْبَيِّنَـٰتِ وَأَنزَلْنَا مَعَهُمُ ٱلْكِتَـٰبَ وَٱلْمِيزَانَ لِيَقُومَ ٱلنَّاسُ بِٱلْقِسْطِ ۖ وَأَنزَلْنَا ٱلْحَدِيدَ فِيهِ بَأْسٌۭ شَدِيدٌۭ وَمَنَـٰفِعُ لِلنَّاسِ وَلِيَعْلَمَ ٱللَّهُ مَن يَنصُرُهُۥ وَرُسُلَهُۥ بِٱلْغَيْبِ ۚ إِنَّ ٱللَّهَ قَوِىٌّ عَزِيزٌۭ - وَلَقَدْ أَرْسَلْنَا نُوحًۭا وَإِبْرَٰهِيمَ وَجَعَلْنَا فِى ذُرِّيَّتِهِمَا ٱلنُّبُوَّةَ وَٱلْكِتَـٰبَ ۖ فَمِنْهُم مُّهْتَدٍۢ ۖ وَكَثِيرٌۭ مِّنْهُمْ فَـٰسِقُونَ - ثُمَّ قَفَّيْنَا عَلَىٰٓ ءَاثَـٰرِهِم بِرُسُلِنَا وَقَفَّيْنَا بِعِيسَى ٱبْنِ مَرْيَمَ وَءَاتَيْنَـٰهُ ٱلْإِنجِيلَ وَجَعَلْنَا فِى قُلُوبِ ٱلَّذِينَ ٱتَّبَعُوهُ رَأْفَةًۭ وَرَحْمَةًۭ وَرَهْبَانِيَّةً ٱبْتَدَعُوهَا مَا كَتَبْنَـٰهَا عَلَيْهِمْ إِلَّا ٱبْتِغَآءَ رِضْوَٰنِ ٱللَّهِ فَمَا رَعَوْهَا حَقَّ رِعَايَتِهَا ۖ فَـَٔاتَيْنَا ٱلَّذِينَ ءَامَنُوا۟ مِنْهُمْ أَجْرَهُمْ ۖ وَكَثِيرٌۭ مِّنْهُمْ فَـٰسِقُونَ - يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ ٱتَّقُوا۟ ٱللَّهَ وَءَامِنُوا۟ بِرَسُولِهِۦ يُؤْتِكُمْ كِفْلَيْنِ مِن رَّحْمَتِهِۦ وَيَجْعَل لَّكُمْ نُورًۭا تَمْشُونَ بِهِۦ وَيَغْفِرْ لَكُمْ ۚ وَٱللَّهُ غَفُورٌۭ رَّحِيمٌۭ - لِّئَلَّا يَعْلَمَ أَهْلُ ٱلْكِتَـٰبِ أَلَّا يَقْدِرُونَ عَلَىٰ شَىْءٍۢ مِّن فَضْلِ ٱللَّهِ ۙ وَأَنَّ ٱلْفَضْلَ بِيَدِ ٱللَّهِ يُؤْتِيهِ مَن يَشَآءُ ۚ وَٱللَّهُ ذُو ٱلْفَضْلِ ٱلْعَظِيمِ -
Indeed, We sent Our messengers with clear proofs, and with them We sent down the Scripture and the balance ˹of justice˺ so that people may administer justice. And We sent down iron with its great might, benefits for humanity, and means for Allah to prove who ˹is willing to˺ stand up for Him and His messengers without seeing Him. Surely Allah is All-Powerful, Almighty. And indeed, We sent Noah and Abraham and reserved prophethood and revelation for their descendants. Some of them are ˹rightly˺ guided, while most are rebellious. Then in the footsteps of these ˹prophets˺, We sent Our messengers, and ˹after them˺ We sent Jesus, son of Mary, and granted him the Gospel, and instilled compassion and mercy into the hearts of his followers. As for monasticism, they made it up—We never ordained it for them—only seeking to please Allah, yet they did not ˹even˺ observe it strictly. So We rewarded those of them who were faithful. But most of them are rebellious. O people of faith! Fear Allah and believe in His Messenger. ˹And˺ He will grant you a double share of His mercy, provide you with a light to walk in ˹on Judgment Day˺, and forgive you. For Allah is All-Forgiving, Most Merciful. This is so˺ that the People of the Book ˹who deny the Prophet˺ may know that they do not have any control over Allah’s grace, and that all grace is in Allah’s Hands. He grants it to whoever He wills. For Allah is the Lord of infinite bounty. (Surah Hadid:25-29)
قُوۡلُوۡٓا اٰمَنَّا بِاللّٰهِ وَمَآ اُنۡزِلَ اِلَيۡنَا وَمَآ اُنۡزِلَ اِلٰٓى اِبۡرٰهٖمَ وَاِسۡمٰعِيۡلَ وَاِسۡحٰقَ وَيَعۡقُوۡبَ وَ الۡاَسۡبَاطِ وَمَآ اُوۡتِىَ مُوۡسٰى وَعِيۡسٰى وَمَآ اُوۡتِىَ النَّبِيُّوۡنَ مِنۡ رَّبِّهِمۡۚ لَا نُفَرِّقُ بَيۡنَ اَحَدٍ مِّنۡهُمۡ وَنَحۡنُ لَهٗ مُسۡلِمُوۡنَ
Say: “We believe in Allah, and in what has been revealed to us and to Abraham, Ishmael, Isaac, Jacob and the descendants (of Jacob) and in what was given to Moses and Jesus and in what the other Prophets received from their Lord. We make no distinction between any of them, and we are those who submit to Allah.” (Surah Baqarah, 2:136)
All the Prophets sent by Allah (SWT) invited men to the same Truth and to the same way. Hence for anyone who is really a lover of Truth it is necessary that he should recognize all of them to be its bearers. Those who believe in one particular Prophet and disbelieve in others do not in fact believe even in that particular Prophet in whom they, claim to believe, for they have not grasped the nature of that universal 'Straight Way' (al-sirat al-mustaqim) which was enunciated by Moses, Jesus and the other Prophets. When such people claim to follow a Prophet they, really mean that they do so out of deference to their forefathers. Their religion in fact consists of bigoted ancestor-worship and blind imitation of inherited customs rather than sincere adherence to the directives of any Prophet of God. The Message of guidance from Allah conveyed to mankind, through His prophets, from time to time, is called the ‘Books of Allah’. All revealed Books except the Holy Qur’an were partly changed by their followers and are not preserved in their original form. As such, the belief of the Muslims in the ‘Books of Allah’ refers solely to the ‘original guidance’ received by their prophets, and not to the present day version of these Books. The text of the Holy Qur’an, however, has always remained unchanged and preserved in its original form.
Belief in the Books implies four things:
1. Firm belief that all of them were revealed from Allah, and that Allah spoke them in a real sense. Some of them were heard from Him from behind a veil, without there being any intermediary from among the angels. Some were conveyed by an angelic Messenger to a human Messenger. Some were written by Allah’s own Hand, as Allah (SWT) says in the Quran -
وَمَا كَانَ لِبَشَرٍ اَنۡ يُّكَلِّمَهُ اللّٰهُ اِلَّا وَحۡيًا اَوۡ مِنۡ وَّرَآىٴِ حِجَابٍ اَوۡ يُرۡسِلَ رَسُوۡلًا فَيُوۡحِىَ بِاِذۡنِهٖ مَا يَشَآءُؕ اِنَّهٗ عَلِىٌّ حَكِيۡمٌ
“It is not given to any human being that Allah should speak to him unless (it be) by Revelation, or from behind a veil, or (that) He sends a Messenger to reveal what He wills by His Leave. Verily, He is Most High, Most Wise.” (Surah 42:51)
وَرُسُلًا قَدۡ قَصَصۡنٰهُمۡ عَلَيۡكَ مِنۡ قَبۡلُ وَرُسُلًا لَّمۡ نَقۡصُصۡهُمۡ عَلَيۡكَ ؕ وَكَلَّمَ اللّٰهُ مُوۡسٰى تَكۡلِيۡمًا ۚ
We revealed to the Messengers We have already told you of, and to the Messengers We have not told you of; and to Moses Allah spoke directly. (Surah 4:164)
وَكَتَبۡنَا لَهٗ فِى الۡاَلۡوَاحِ مِنۡ كُلِّ شَىۡءٍ مَّوۡعِظَةً وَّتَفۡصِيۡلًا لِّـكُلِّ شَىۡءٍ ۚ فَخُذۡهَا بِقُوَّةٍ وَّاۡمُرۡ قَوۡمَكَ يَاۡخُذُوۡا بِاَحۡسَنِهَا ؕ سَاُورِيۡكُمۡ دَارَ الۡفٰسِقِيۡنَ
We wrote for him on the Tablets ˹the fundamentals˺ of everything; commandments and explanations of all things. ˹We commanded,˺ “Hold to this firmly and ask your people to take the best of it. I will soon show ˹all of˺ you the home of the rebellious. (Surah 7:145)
2. The Books that Allah has mentioned by name, we must believe in by name.
These are the Books which Allah has named in the Quran, i.e., the Quran, the Tawrat, the Injeel (Gospel), the Zaboor (Psalms), and the Scriptures of Ibrahim and Musa. Allah (SWT) says in the Quran -
فَلِذٰلِكَ فَادۡعُ ۚ وَاسۡتَقِمۡ كَمَاۤ اُمِرۡتَۚ وَلَا تَتَّبِعۡ اَهۡوَآءَهُمۡۚ وَقُلۡ اٰمَنۡتُ بِمَاۤ اَنۡزَلَ اللّٰهُ مِنۡ كِتٰبٍۚ وَاُمِرۡتُ لِاَعۡدِلَ بَيۡنَكُمُؕ اَللّٰهُ رَبُّنَا وَرَبُّكُمۡؕ لَـنَاۤ اَعۡمَالُـنَا وَلَـكُمۡ اَعۡمَالُكُمۡۚ لَا حُجَّةَ بَيۡنَنَا وَبَيۡنَكُمُؕ اَللّٰهُ يَجۡمَعُ بَيۡنَنَاۚ وَاِلَيۡهِ الۡمَصِيۡرُؕ
(This being so, O Muhammad), call people to the same religion and be steadfast about it as you were commanded, and do not follow their desires, and say (to them): “I believe in the Book Allah has sent down. I have been commanded to establish justice among you. Allah is our Lord and your Lord. We have our deeds and you have your deeds. There is no contention between us and you. Allah will bring us all together. To Him all are destined to return.” (Surah 42:15)
In the above Ayat, Do not follow their desires, that is, do not make any change nor effect any increase or decrease in this religion only to please them. Do not resort to any compromises with the misguided people on the principle of give and take. Do not make any room in the religion for their whims, prejudices and practices of ignorance in the hope that they would embrace Islam. Let the one who wants to accept, accept the original, pure religion of God, as sent down by Him, straight forwardly; otherwise let him go and enter any hell that he chooses for himself. The religion of God cannot be changed for the sake of the people; if the people are desirous of their own well being and true success, let them change their ways and mold themselves according to it.
3. Believing whatever is true of what they say, such as what is said in the Quran, and whatever has not been altered or distorted in the previous Books.
4. Believing that Allah revealed the Quran as a witness over these Books and to confirm them. As mentioned in the Quran -
وَاَنۡزَلۡنَاۤ اِلَيۡكَ الۡكِتٰبَ بِالۡحَـقِّ مُصَدِّقًا لِّمَا بَيۡنَ يَدَيۡهِ مِنَ الۡكِتٰبِ وَمُهَيۡمِنًا عَلَيۡهِ فَاحۡكُمۡ بَيۡنَهُمۡ بِمَاۤ اَنۡزَلَ اللّٰهُ وَلَا تَتَّبِعۡ اَهۡوَآءَهُمۡ عَمَّا جَآءَكَ مِنَ الۡحَـقِّؕ لِكُلٍّ جَعَلۡنَا مِنۡكُمۡ شِرۡعَةً وَّمِنۡهَاجًا ؕ وَلَوۡ شَآءَ اللّٰهُ لَجَـعَلَـكُمۡ اُمَّةً وَّاحِدَةً وَّلٰـكِنۡ لِّيَبۡلُوَكُمۡ فِىۡ مَاۤ اٰتٰٮكُمۡ فَاسۡتَبِقُوا الۡخَـيۡـرٰتِؕ اِلَى اللّٰهِ مَرۡجِعُكُمۡ جَمِيۡعًا فَيُنَبِّئُكُمۡ بِمَا كُنۡتُمۡ فِيۡهِ تَخۡتَلِفُوۡنَۙ
Then We revealed the Book to you (O Muhammad!) with Truth, confirming whatever of the Book was revealed before, and protecting and guarding over it. Judge, then, in the affairs of men in accordance with the Law that Allah has revealed, and do not follow their desires in disregard of the Truth which has come to you. For each of you We have appointed a Law and a way of life. And had Allah so willed, He would surely have made you one single community; instead, (He gave each of you a Law and a way of life) in order to test you by what He gave you. Vie, then, one with another in good works. Unto Allah is the return of all of you; and He will then make you understand the truth concerning the matters on which you disagreed. (Surah 5:48)
In Arabic, haymana, yuhayminu, hayamanah signify 'to protect, to witness, to keep trust, to back and to support'. The expression 'haymana al-rajul al-shay' means that the man protected and guarded the thing. Likewise, 'haymana al-ta'ir 'alafirdkhih' means that the bird took its young ones under the protection of its wings. Once 'Umar said to the people: 'Inni da'in fa hayminu' ('I am praying; support me by saying amen'). To say that the Qur'an is muhaymin of al-kitab means that it preserves all the true teachings of the earlier divine books; that it has secured them from loss. The Qur'an also confirms those Books in that the contents of the Qur'an testify to the truth of those parts which are indeed from God. The Qur'an is, further, a witness over those Books in the sense that, with its help, the elements which embody true revelations from God can be distinguished from the accretions which have corrupted them. Whatever in these Books accords with the Qur'an is from God, and whatever is not in conformity with it is from human beings.
The mufassirin (commentators) said that Muhaymin means trustworthy and a witness over the Books that came before it, and confirming them, i.e., confirming whatever is true in them and rejecting whatever alterations, distortions and changes have occurred in them, and ruling that the previous rulings have been abrogated – i.e., they are no longer applicable – and that new rulings and laws have been promulgated. Hence all those who were following previous books and who have not turned on their heels should submit to it, as Allah says -
ٱلَّذِينَ ءَاتَيْنَـٰهُمُ ٱلْكِتَـٰبَ مِن قَبْلِهِۦ هُم بِهِۦ يُؤْمِنُونَ - وَإِذَا يُتْلَىٰ عَلَيْهِمْ قَالُوٓا۟ ءَامَنَّا بِهِۦٓ إِنَّهُ ٱلْحَقُّ مِن رَّبِّنَآ إِنَّا كُنَّا مِن قَبْلِهِۦ مُسْلِمِينَ -
˹As for˺ those ˹faithful˺ to whom We had given the Scripture before this ˹Quran˺, they do believe in it. “And when it is recited to them, they say: We believe in it. Verily, it is the truth from our Lord. Indeed even before it we have been from those who submit themselves to Allah in Islam as Muslims.” (Surah 28: 52-53)
It is obligatory for all the ummah (followers of Muhammad) to follow the Quran both outwardly and inwardly, and to adhere to it, and give it its due, as Allah says -
وَهَـٰذَا كِتَـٰبٌ أَنزَلْنَـٰهُ مُبَارَكٌۭ فَٱتَّبِعُوهُ وَٱتَّقُوا۟ لَعَلَّكُمْ تُرْحَمُونَ -
This is a blessed Book We have revealed. So follow it and be mindful ˹of Allah˺, so you may be shown mercy. (Surah 6:155)
What is meant by adhering to the Quran and giving it its due is: regarding what it permits as permitted, regarding what it forbids as forbidden, obeying its commands, avoiding that which it prohibits, paying heed to its lessons, learning from its stories, understanding its clear and unambiguous texts, referring the exact meaning of its ambiguous texts to Allah, not overstepping its limits and defending it, whilst memorizing it, reciting it in a proper manner, pondering the meanings of its verses, reciting it in prayer night and day, being sincere towards it in all senses, and calling others to do likewise with understanding.
This belief will bear great fruit for a person, the most important of which is:
1. Knowledge of Allah’s care for His slaves, for He has revealed to each people a Book by which they may be guided.
2. Knowledge of the wisdom of Allah in the laws which He has set out for each people, laws which are suited to their circumstances as Allah says - “To each among you, We have prescribed a law and a clear way.” [5:48].
3. Fulfilling the duty of giving thanks to Allah for this great blessing.
4. The importance of paying attention to the Quran, by reading it, pondering its meanings, understanding its meanings and acting accordingly.
Rest Allah (SWT) knows best.
Source: Quran, Tafsir Ibn Katheer, In the shade of the Quran, Islam Q&A