If someone (a non-Muslim) should argue with us and ask for reasons to demonstrate the truth of Islam, we could prove it through the eternal miracle of the Qur'an, and by reference to its miraculous nature, as we have explained before.

Here however, it is our intention to satisfy our own minds, in the event that we should wish to find assurance concerning the truth of Islamic ;for sometime it happens that such a question arises on the mind of a liberal-thinking man, when he desires to strengthen his faith.

As for the previous religious such as Judaism and Christianity, there is no way to prove the truth of them or to satisfy ourselves or anyone else who doubts them, without there being faith in Islam ; for they have no eternal miracle like the Qur'an. And the miracles of the former prophets which their followers bring forward as evidence are unacceptable, because the variety of the narration is suspect. The books of the former prophets which have been handed down to us, that is to say the books which are related to these prophets such as the Torah and the Gospels, are in no way an eternal miracle which can be put foreword as a convincing reason for the truth of their religious, which nevertheless, have been confirmed by Islam.
It is clear that when we accept and believe in Islam, we must also believe in whatever it has brought and confirmed, and one of its teachings is the prophethood of many previous prophets, as we have described above. It therefore follows that a Muslim, after he has accepted the teachings of Islam, is not required to evaluate the truth of Christianity or Judaism or other such religions, because belief in Islam necessarily entails belief in the former religions and prophets. What is more, the Muslim does not need to verify the truth of the miracles of the former prophets.

However, if someone investigates the Islamic religion, but is not convinced of it, it is incumbent on him, as a rational necessity, to evaluate the truth of christianity, because it is the last religion previous to Islam. Then if he is not convinced by christianity he must consider Judaism, because it is the religion previous to Christianity and Islam, and he must continue in this way until he finds a religion about whose truth he feels certain.
By similar reasoning, it is clear that someone who has grown up believing in Judaism or Christianity must consider other religions to which people have been called by a prophet who came after their own prophet. for example. For example, the Jews must evaluate Islam and Christianity according to what was said previously about the necessity to consider religions rationally, and Christians must consider the truth of Islam. It follows neither of them can be excused for believing in their own religions while ignoring the subsequent religions because there is nothing in Judaisms and Christianity which could contradict these religions, for neither Musa (A.S) nor 'Isa (A.S) stated that no prophet would come after them. It is surprising how christians and Jews can be sure in their belief and in their religions without considering the truth of the subsequent and last religion.
Wisdom dictates that the weight the truth of the subsequent religion or religion. And if the truth is not established, then they should continue with their original beliefs. The Muslim, on the other hand, as we stated earlier, because of his belief in Islam, has no need to consider the truth of the previous religions or of any future ones. As for the previous religions Islam has confirmed them: however; the Muslim should not follow their commandments or their books, because Islam has superseded them. And as regards future religions,the Holy Prophet of Islam, Muhammad (A.S) said:

No prophet will come after me.

Since in the eyes of a Muslim the Prophet is honest and truthful, and as Allah has said:

Nor does he speak from his own desire. This is nought but a revelation (53;3-4)