Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
What is meant by the Gospel and the Torah is to establish them as revealed by Allah, and what is falsified, changed or abrogated was not meant by the verse of Allah. Ibn Taymiyah in al-Jawab al-Sahih stated that they (the Jews and Christians) were not ordered to establish what had been abrogated.
Therefore, it is more appropriate that they were not ordered to comply by what was forged. In addition to this, it would not have been possible to establish these Books without abiding by what was revealed to them which is the Qur'an.
As Allah Says (interpretation of meaning) at the end of the verse: {…till you act according to the Taurât (Torah), the Injeel (Gospel), and what has (now) been sent down to you from your Lord (the Qur'ân)."…..}[5:68]. What is meant by “what has been revealed to you” is the Qur'an.
The evidence supporting the reason this verse had been revealed is that they claimed that they were on the truth and that they acted according to what was revealed in their books. So Allah responded to them that they were upon nothing until they acted upon the Torah, the Gospel and the Qur'an, and not distinguish between the Prophets and Books.
Ibn Jarir al-Tabari said about the interpretation of the meaning of the verse: Say, O People of the Book, you are indeed upon nothing, i.e. of what you claim to be upon that Musa (Moses) brought to you, O, you Jews, or that Issa (Jesus) brought to you, O, you Christians, until you act upon the Torah and the Gospel and what has been revealed to you from your Lord, that Muhammad (Sallallahu Alaihi wa Sallam) has brought to you, in the Furqan. So until you act upon all this and believe in what is in them, like the belief in Muhammad (Sallallahu Alaihi wa Sallam), and the acknowledgement that what he brought is the truth, confessing that all that, is from Allah. Do not deny anything which is contained in the Qur’an, and do not distinguish between the Prophets of Allah, believing in some and not believing in others. If you deny one of them, you are denying (disbelieving in) all of them.’
In addition to this, Ibn Abbas is reported to have said: The Prophet (Sallallahu Alaihi wa Sallam) came to Rafi’ Bin Haritha, Sallaam Bin Mishkam, Malik Bin al-Sayf, and Rafis Bin Harimla, all of whom were Jews, all of whom were Jews, and they told him: ‘O Muhammad, do you not claim that you are upon the belief and religion of Abraham, and believe in what we have in the Torah, and confess that it is the truth from Allah; the Prophet (Sallallahu Alaihi wa Sallam) said: “Of course I do, but you have innovated and denied what is in it from the pact which was agreed with you, and concealed what you were ordered to convey to the people, and I am innocent of and exempt from what you innovated.’ They said: ‘We act upon what we have in our hands, we are upon the truth and guidance, and we do not believe in you and we do not follow you. Then Allah revealed: {Say (O Muhammad SAW) "O people of the Scripture (Jews and Christians)! You have nothing (as regards guidance) till you act according to the Taurât (Torah), the Injeel (Gospel), and what has (now) been sent down to you from your Lord (the Qur'ân)." Verily, that which has been sent down to you (Muhammad SAW) from your Lord increases in many of them their obstinate rebellion and disbelief. So be not sorrowful over the people who disbelieve.}[5:68].