After the coming of the Prophet Muhammad (peace and blessings of Allah be upon him), there is a further distinction that needs to be made concerning the religion of “Islam.” 

Before the time of the Prophet (peace and blessings of Allah be upon him), one could say that there were many “Islams.” That is, each people had their prophets, followed their teachings and were on the path of Islam. At the same time, if a new prophet in the same line of prophets came to them, they had no choice but to follow that new prophet. The one who would refuse to accept Allah’s later prophet is not truly submitting to Allah. If he is not truly submitting to Allah, then he is not a “Muslim.” 

There are two very important points that demonstrate the relationship between the way of the Prophet Muhammad (peace and blessings of Allah be upon him) and the way of the true prophets before him.

 First, the way of the Prophet Muhammad abrogates the previous laws. 

Second, by the wisdom of Allah, Allah did not allow the teachings of the previous prophets to remain preserved in a completely undistorted manner.

Allah says

And We have sent down to you (O Muhammad) the Book in truth, confirming the Scripture that came before it and a witness over it (old Scriptures). So judge between them by what Allah has revealed, and follow not their vain desires, diverging away from the truth that has come to you

(5:48)

This verse demonstrates that the Quran has been revealed in truth and confirms what has been revealed beforehand of the revelations and it is a judge and witness over the previous books. In other words, it preserves, protects and witnesses to the truth found in the earlier revelations. 

At the same time, though, it shows the falseness of the distortions that have been done to the previous revelations. Anything that is in conformity with the Quran is true and anything that contradicts the Quran must be false. Thus, the Quran has been revealed to affirm what has been preserved of the earlier revelations while correcting any distortions. 

A clear example of this nature has to do with the supposed crucifixion of Jesus Christ. This supposed act is the entire basis for raising the Prophet Jesus (peace and blessings of Allah be upon him) to the level of God. The Quran’s view on this issue however is very clear:

And because of their saying (in boast), ‘We killed Messiah Jesus, son of Maryam (Mary), the Messenger of Allah,’ - but they killed him not, nor crucified him, but the resemblance of Jesus was put over another man (and they killed that man), and those who differ therein are full of doubts. The have no (certain) knowledge, they follow nothing but conjecture. For surely; they killed him not

(4:157)

Distortion of the earlier books has been alluded to in numerous places in the Quran. For example,

Allah says in reference to the People of the Book

“Then woe to those who write the Book with their own hands and then say, ‘This is from Allah,’ to purchase with it a little price! Woe to them for what their hands have written and woe to them for that they earn thereby”

(2:79)

and “And verily, among them is a party who distort the Book with their ton-gues, so that you may think it is from the Book, but it is not from the Book, and they say:

This is from Allah,’ but it is not from Allah; and they speak a lie against Allah while they know it

(3:78)

Therefore, the Prophet said,

Do not affirm what the People of the Book say nor deny them. Instead, say, ‘We believe in what has been revealed to us what has been revealed to you. Our God and your God is one and we submit to Him as Muslims

by al-Bukhari

It is interesting to note that the only religion that has kept the name “submission to Allah” or Islam is that of the final Prophet Muhammad (peace and blessings of Allah be upon him). The other well-known religions are all named after individuals, peoples or places. According to Microsoft Encarta, the term Judaism did not even exist in pre-modern Hebrew. It is in reference to Judah. Christianity is, of course, named after Christ as Buddhism is named after Buddha. Hinduism has to do with the place, Hindustan. But, by Allah’s wisdom and mercy, the name of the only true religion of submission to Allah—the religion of all the prophets—has been preserved and kept only in reference to the mission of the final prophet who was sent for all of humanity. 

As a final note, although the message of the Prophet Muhammad is nothing but a continuation of the message of the earlier prophets, Christians and Jews are in no way to be coerced to embrace Islam or to follow its teachings.

Allah says

There is no compulsion in religion. Verily, the Right Path has become distinct from the wrong path. Whoever disbelieves in false gods and believes in Allah, then he has grasped the most trustworthy handhold that will never break. And Allah is All-Hearer, All-Knower

(2:256)

They should, though, be called to the truth of Islam and invited to follow the Prophet Muhammad (peace and blessings of Allah be upon him).