By Omar KN
1. - Earlier revelations, such as the Torah, the New Testament, and sacred scriptures such as the Hindu Vedic Scriptures, or the Teachings of the Buddha have but come to a certain people or limited area at a certain time in history, whereas the message of Islam has been given to mankind in general, everywhere, until the end of times.
2. - Those religions have already reached and passed their zenith, their highest point of realization.
Islam however, despite some recent modernist tendencies, is still a living tradition linking back to its prophetic source and is therefore still valid - and will be - until the Day of Judgement.
3. - What happened to those previous religions is that on the one hand their doctrins or teachings were changed or forged so that they became faulty and diluted – either intentionally – to the detriment of all those believers who sought reliable divine guidance – or on the other hand 'unintentionally' through their neglect of the doctrines when their representatives stopped paying attention to them and stopped living up to those teachings.
Because of the alterations to the original message of their respective revelations, their sanctifying power and Divine blessings to guide man aright diminished more and more, if not disappeared completely.
This is one of the reasons why the message of Islam (accepting the will of Allah by following the pattern of the Prophet ﷺ ) was revealed to mankind, to restate the original message and to establish an authentic spiritual link from the Messenger of Allah ﷺ .
4. - What had been revealed through earlier traditions (see above) has essentially become 'absorbed' into the Islamic teaching. The Islamic doctrine is general and encompassing, it is to be applied generally in space and time while its landmark is encompassing Divine Mercy and Compassion (rahmah); it is a confirmation and clarification of what came before (of Divine revelations), answering any existential problem or situation of ancient man as well as of modern man and his society.
5. - Concerning what is sometimes called 'the transcendant unity of religions':
traditional Islam does not use this term, because it can lead to misunderstandings. However it is correct to say that the world-religions do have common 'core principles', because these principles are eternal, from a Divine Origine and therefore according to the Truth. Then these items of faith have to be checked.
• Faith in God, or a supernatural eternal Being, in the next life beyond this one, and in holy scriptures.
• However, the fact that we see these common principles DOES NOT MEAN that all religions are somehow the same or equally valid, they are neither the same nor equally valid. As individual man or woman, one has to live by the last of the revealed religions: Islam, which has - as shown above - superceded the earlier traditions. And it did abrogate those earlier religions because of God saying so Himself  and also because of the authenticity of its message or revelation. 
Furthermore it is not enough to have a mental attitude of 'knowing' the metaphysical doctrines, without realizing the message individually and personally, ie. without being guided by this 'knowledge' to act accordingly: The Prophet of Allah ﷺ called Islam faith, prayers and actions [for the pleasure of God] . Otherwise it is only question of rational, discursive knowledge, without spiritual advancement, which is worse than not knowing about it in the first place:
The intention is that the fulfillment of the Shariʿa may lead to the haqiqah (Divine Truth).'
Here we may say this Duʿa:
Allahumma thabbit qulūbana ʿalaa taʿātika
O Allah! Strengthen our hearts for our obedience to You
7. - It is not the position of any of the Shuyūkh of orthodoxy (traditional Islam), to claim that non-Islamic religions are valid. However it is true that all religions which believe in all prophets and in all the revelations coming to them through the Creator, are the same and the target of all religions is the same, but the methods have changed throughout times.' (see 5.)
8. - The Sacred Law of the Prophet ﷺ superseded …
"The Sacred Law of the Prophet ﷺ superseded all previously valid religious laws, it was identical with them in beliefs." 
"Only Islam is valid or acceptable now that Allah has sent it to all men."
"The religious laws shara'i' are all lights, and the law of Muhammad ﷺ Allah bless him and give him peace) among these lights is as the sun's light among the light of the stars:
If the sun comes out, the lights of the stars are no longer seen and their lights are absorbed into the light of the sun: the disappearance of their lights resembles what, of the religious laws, has been abrogated nusikha by his law despite their existence, just as the lights of the stars still exist.
This is why we are required by our universal law to believe in all prophetic messengers rusul and to believe that all their laws are truth, and did not turn into falsehood by being abrogated: that is the imagination of the ignorant.
So all paths return to look to the Prophet's path ﷺ (Allah bless him and give him peace): if the prophetic messengers had been alive in his time, they would have followed him just as their religious laws have followed his law.
For he was given Comprehensiveness of Word jawāmi' al-kalīma, and given [the Koranic verse] 'Allah shall give you an invincible victory' (Koran 48:3), 'the invincible' [al-ʿazīz, also meaning rare, dear, precious, unattainable] being he who is sought but cannot be reached.
When the prophetic messengers sought to reach him, he proved impossible for them to attain to--because of his [being favored above them by] being sent to the entire world bi'thātihi al-'amma, and Allah giving him Comprehensiveness of Word jawāmi' al-kalīma, and the supreme rank of possessing the Praiseworthy Station al-maqām al-maHmūd in the next world, and Allah having made his Nation umma 'the best Nation ever brought forth for people' (Koran 3:110). The Nation of every messenger is commensurate with the station of their prophet, so realize this.
(al-Futuhat al-Makkiyya, III 153.1220).
9. - Chittick's 'misunderstanding':
It was also shown by Shaykh Nuh H M Keller  “that Chittick's claim above that Ibn al-ʿArabi "does not draw the conclusion that many Muslims have drawn -- that the coming of Islam abrogated (naskh) previously revealed religions" is false”, as is seen from the above quote by Ibn al-ʿArabi, which Chittick is neglecting. (See chapter 2 at Nuh H M Keller's page  ).
If Chittick holds that "it is true that many Muslims believe that the universality of guidance pertains only to pre-Koranic times, but others disagree; there is no 'orthodox' interpretation here that Muslims must accept" (Chittick, Religious Diversity, 124).
This then is his personal opinion, which is not of traditional Islam, but "orthodoxy exists, it is unanimously agreed upon by the scholars of Muslims..."
Here no muslim scholar would disagree.
There are of course those who hold unorthodox positions, but they should not be overestimated, and everyone of them will be judged for their interpretations and erroneous opinions.
10. - Difference between Divine Will and Divine Acceptance
One has to distinguish between the Will of Allah that there may exist different religions in the world at the same time and the Divine Acceptance of only Islam:
"So at the level of creation and destiny, everything is the will of God, and in a sense, all religions, according to ʿAbd al-Qadir's viewpoint, are "worship" of the Deity. But at the level of validity and salvation, only the worship that conforms to what the prophets (upon whom be peace) have brought is acceptable to Allah." 
11. - The wider sense of the word 'Islam'
We have to understand the word Islam here* in its wider sense for the Quran affirms that Jesus (a.s.) and his companions were Muslims and it says the same for every messenger of religion and his first followers.
* Surely the true religion with ALLAH is Islam.
Sura Al-ʿImrān 3-19
* And when Jesus perceived their disbelief, he said, 'Who will be my
helpers in the cause of Allah?' The disciples answered, 'We are the
helpers of Allah. We have believed in Allah. And bear thou witness that we
are obedient (lit.: that we are Muslims).'
Sura Al-ʿImrān 3-52
So there is 'Islam' in this wider sense, surrender to the will of Allah and also 'Islam' in the sense of the dīn of the revelation of the Quran and the tradition of Prophet Muhammad ﷺ , which we follow, in order to be saved.
The Quran elucidates that Jesus and all other prophets were muslims who proclaimed the Divine message of Islam. They taught their peoples at different periods in human history, and although their messages did not contain the laws of today's Islam, their essential content was the same:
• Worship of one true God and submission to His will.
• Retribution in the Hereafter of both good and bad.
This fact has been misunderstood and ignored by all those who don't understand the notion of Islam in its wider meaning. Because - apart from being the name of (the teachings) proclaimed by Prophet Muhammad ﷺ - Islam is a state of mind and a guide for action.
This is what is aimed at by the following quranic verse:
* O ye who believe! fear Allah as He should be feared; So this religion is not a new religion, or a new message, but it represents the sum and summit of all the earlier messages and a correction of the deviations which had occurred over time. 12. - A very good approach to open the mind of modern man to the spiritual truth of Islam, is the disposition of the metaphysical doctrines by Shaykh ʿAbd Al Wahid Yahya, René Guénon. He analysed as no-one before him the mentality of the modern West which evolved out of the decadence of its religion, and provided the intellectual tools to uncover anti-traditional so-called spiritual movements. Today when the modern world is in great crisis, all kinds of 'New Age'-movements and other anti-traditional trends seek to make matters worse. (See for example: Eleven (False) New Age Principles) If others have come after him, to speak as of him, but without authority, then this is their resposibility We should be careful attributing from here-say and may Allah protect us from falling into error.
Peace and blessings upon our leader and master,
and let not death overtake you except when you are in a state of submission (lit.: except that you are Muslims).
Sura 3, verse 102
Sayyiduna Muhammad, ﷺ and his family and his followers.
So this religion is not a new religion, or a new message, but it represents the sum and summit of all the earlier messages and a correction of the deviations which had occurred over time.
12. - A very good approach to open the mind of modern man to the spiritual truth of Islam, is the disposition of the metaphysical doctrines by Shaykh ʿAbd Al Wahid Yahya, René Guénon.
He analysed as no-one before him the mentality of the modern West which evolved out of the decadence of its religion, and provided the intellectual tools to uncover anti-traditional so-called spiritual movements. Today when the modern world is in great crisis, all kinds of 'New Age'-movements and other anti-traditional trends seek to make matters worse. (See for example: Eleven (False) New Age Principles)
If others have come after him, to speak as of him, but without authority, then this is their resposibility We should be careful attributing from here-say and may Allah protect us from falling into error.
Peace and blessings upon our leader and master,
Peace and blessings upon our leader and master,
الصَّلاَةُ لِوَقْتِهَا، وَبِرُّ الْوَالِدَيْنِ، ثُمَّ الْجِهَادُ فِي سَبِيلِ اللَّهِ
(1) To perform the (daily compulsory) prayers at their (early) stated fixed times,
(2) To be good and dutiful to one's own parents.
(3) and to participate in Jihad in Allah's Cause."
(Narrated by Ibn Mas'ud; sunnah.org )
• Book Review: The Study Quran, by Dr. Gibril F Haddad
• Book Review: Followup on the Study Quran, Dr. GF Haddad