Given the fact that ‘Eesa (Jesus), may Allaah exalt his mention, will descend to the earth shortly before the Day of the Resurrection, is it possible, from an Islamic point of view, for a person to combine two religions, Islam and Christianity?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If the questioner means by combining Islam and Christianity what is being propagated lately under the name of "the unity of religions," which means mixing different religions together and considering them to be one religion that combines the Islamic, Christian and Jewish creeds, this is manifest disbelief and explicit apostasy. This is because a Muslim does not have sound, integral, Islamic creed unless he testifies to the monotheism of Allaah The Almighty and disbelieves anything that is worshipped besides Allaah The Exalted. In this regard, Allaah the Almighty Says (what means): {So whoever disbelieves in Taaghoot and believes in Allaah has grasped the most trustworthy handhold with no break in it.} [Quran 2: 256] Therefore, how is it possible to merge Islamic monotheism and the polytheism of the Trinity?

On the other hand, if the questioner is trying to refer to "inter- religion dialogue" and arguing in a way that is best, in this case it is permissible. Referring to this, Allaah the Exalted Says (what means):

•        {And do not argue with the People of the Book except in a way that is best} [Quran 29: 46] 

•        {Say, "O People of the Book, come to a word that is equitable between us and you} [Quran 3: 64]

It is a fact that  ‘Eesa the son of Maryam (Mary), may Allaah exalt her mention, will descend at the end of this life. However, he will judge according to the Islamic Sharee'ah (Islamic law), not the Christian or Jewish ones. As Islam is the religion of all prophets, may Allaah exalt their mention, and Allaah The Almighty never accepts any other religion, ‘Eesa will judge according to Islam after his descent.   

Referring to this, it was reported that the Prophet, sallallahu ‘alayhi wa sallam, swore that ‘Eesa the son of Maryam, may Allaah exalt her mention, would descend as a judge and a just person, and he would break the cross, kill the swine, nullify the Jizyah (levy paid by non-Muslim subjects in an Islamic state) and accept Islam only. [Al-Bukhari]  Commenting on the Hadeeth, Ibn Hajar mentioned that he would nullify the Christian religion at this time.

Allaah Knows best.