Jesus asked who would support him for the cause of Allah (swt) when he realized that they disbelieved despite all the sign confirming that he was honest.
(… قَالَ الْحَوَارِيُّونَ نَحْنُ أَنصَارُ اللَّهِ …) (…The disciples said, “We are supporters for Allah …): The disciples were the supporters of both Allah and Jesus Christ (PBUH). The meaning of this word ‘disciples’ (in Arabic) is the people whose faces are fresh and shining with faith.
( آمَنَّا بِاللَّهِ وَاشْهَدْ بِأَنَّا مُسْلِمُونَ … ) (…We have believed in Allah and testify that we are Muslims [submitting to Him): Their belief in the Almighty is a proof of their support. They believed in and followed the orders of Allah the Almighty, then, asked Jesus (PBUH) to testify the same.
In this context, all the religions revealed since the time of Adam (PBUH) thru the last of the prophets and messengers are Islam. The Islamic Sharia, on the other hand, is what’s revealed by the Holy Quran and to Prophet Muhammad (saws). This verse: {and testify that we are Muslims [submitting to Him].} is a proof of that. Thus, we have a unity of the parades of faith. However, someone may wonder: why do we have the Gospel, the Torah, the Quran, the Zabur, the scriptures of Abraham, and so on as long as all the heavenly books have the same issues with respect to paradise, hell, reckoning, punishment, parables, and history? Why don’t we have one book? The answer is that the human mind develops over time, and the time, whereabout, and environment of the call of the prophets differs, causing the legislations to differ. Therefore, a legislation that is in line with such development is a must till there is a final Sharia (legislation) that encompasses every time and everywhere, and all the previous prophets and messages. This is the Holy Quran, the final of the heavenly books by the Almighty. In conclusion, all the rules related to humans differ from one message to another, whereas the faith, informing, and statements by the Almighty with respect to the past prophets and incidents are in the same sphere.