The foregoing is significant for at least two reasons. First, Surah 3:81 is presupposing that the previous Scriptures, i.e. the Holy Bible, are the criteria determining whether a person is a true or false prophet. The author of the Quran essentially accepted the fact that all messengers must be in full agreement with the teachings of the Holy Bible, otherwise they would be rejected.
Second, the only way for Muhammad or anyone else claiming to be a messenger to be able to confirm the previous Scriptures is if these Books remained intact. If these texts were corrupted then the messenger wouldn’t be able to confirm them lest he be guilty of verifying scriptures that God had not inspired. And yet failing to confirm the Scriptures in the possession of the people before him would lead to a complete rejection of such a messenger. The people would consider such a person a false messenger for contradicting the Scriptures in their possession which they would view as being the uncorrupt revelations of God!
To put it in another manner, the only way for the community of the prophets such as the Jews and Christians to know whether someone like Muhammad was a messenger is if he confirmed their Holy Scriptures. But if these Scriptures had been corrupted then there would be no way for the people to know who that messenger was since they no longer had the authentic Scriptures for him to confirm. This would lead them to conclude that such a person was a false messenger for not confirming their religious texts!
It should not be hard for Muslims to see why this reasoning is valid. Just imagine another man coming today, claiming to be a prophet (or some other title to the effect that he is speaking with divine authority), and saying exactly what Muhammad said, i.e. he came to confirm what the earlier prophets said. Would Muslims accept him as a prophet because he claims to confirm what Muhammad had already said? The Muslim answer would obviously be no, since that person must not contradict the teachings of the Quran or Muhammad, and yet by claiming to be a prophet he would be contradicting the Quran’s testimony that Muhammad is the seal of the prophets.
In fact, isn’t that what Baha’ullah (founder of the Baha’is) and Mirza Ghulam Ahmad (founder of the Ahmadiyya) did? Both acknowledge (confirm) Muhammad as a prophet and the Quran as divine revelation, but they are adding their own words to it. Their additional writings are foundational for the movements they have started. Yet Muslims reject them as false. Why would they if these men satisfy this quranic criterion of confirming the revelation that came before them?
Just as Christians do, Muslims test the later claims to prophethood with the former revelation — and they are right in doing so. That has to be the principle.
The foregoing leaves Muslims in a quagmire. If the Quran is to be believed then Muslims must accept the fact that the previous Scriptures have been preserved and Muhammad had to confirm them as true revelations. Yet, since these previous Scriptures of the Jews and Christians (i.e. the Holy Bible) contradict the teachings of the Quran and Muhammad on essential issues, this therefore means that Muhammad is a false prophet.
In conclusion, Muhammad fails the very biblical criterion – accepted by the Quran itself – for determining whether a person is a true prophet or not.
Confirming means confirming that the Prophets received the revelation,confirming does not mean that those revelations were never corrupted or forged.
When you buy the 22nd edition of a book of Medicine,it means that you are confirming the previous editions,or the fact that there were 21 other editions too.
Confirming does not mean that you affirm the knowledge in the previous editions or you must be agreeing to it.
Being a Muslim we confirm the previous scriptures,we confirm their revelation by God,but we also know that they are now corrupted.