Most of Jews, Christians and idolaters will become Muslims, when they see the correct explanation of the Quran brought to them by the Awaited Mahdi
Then they will realize that the Quran is the true and authentic word of God; at that time most of them will believe

God - be glorified - said in the Quran 96: 1
لَمْ يَكُنِ الَّذِينَ كَفَرُوا مِنْ أَهْلِ الْكِتَابِ وَالْمُشْرِكِينَ مُنفَكِّينَ حَتَّى تَأْتِيَهُمُ الْبَيِّنَةُ

The explanation

(Those who unbelieve among [Jews and Christians:] the people of the Bible [lit. Scripture] and [among] the associaters [of the Arab and others] will not desist [from their unbelief] until there shall come to them [the Mahdi or the Paraclite with] the clear explanation [of the Quran, and then most of them will believe.])