From the viewpoint of the holy Qur’an and authentic Shia traditions, Jesus Christ is not dead, and wasn’t crucified at all. He is alive and the Christians, of that time, were led into error about him while Allah took him up to Himself:
“And they did not kill him nor did they crucify him, but it appeared to them so………nay! Allah took him up to Himself.” (Qur’an, 4:157&158)
In the Shia traditions it has come down that he lives in the fourth heaven. What is the fourth heaven? It isn’t very clear.
Secondly, according to the context of numerous Shia and Sunni traditions, Jesus Christ is Hazrat Mahdi’s vizier (minister). This messenger of Allah would follow Hazrat Mahdi (a.t.f.s.) and pray behind him.
Thirdly, right from the time of the holy Prophet’s appointment, Jesus Christ acts upon Islam, the holy Qur’an and the way of the holy Prophet (s.a.w.a.). The fact that he shoulders Imam Mahdi’s ministry supports this matter as well.
Fourthly, the Christians, too, are like other nations, and majority of them would positively respond to the call of monotheism and justice given by the promised saviour. Like few others, few amongst them would show resistance.
Based on traditions, the interpreters have interpreted verse 159 from Chapter Nisa (“And there is not one of the followers of the Book but most certainly believes in this before his death” ) as follows:
Before the resurrection day (at the time of rising of Imam Mahdi), Jesus Christ would descend and no Christian or Jew would remain but that they would bring faith in him.
Therefore, as per this interpretation and some traditions, the people of the Book would all bring faith in him during the end of time and Hazrat Mahdi’s rule.