Why are Muslims allowed to marry Christians and not Hindus even though the former worship Jesus, a human being, in the form of idols, statues, etc., which falls into the category of idol worship?
“…The food (slaughtered cattle, eatable animals) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time, when you have given their due Mahr (bridal-money given by the husband to his wife at the time of marriage), desiring chastity (i.e. taking them in legal wedlock) not committing illegal sexual intercourse, nor taking them as girlfriends…” 
This is a special concession made in the Qur’an, stated to the Prophet (ﷺ), for Christians and Jews, because of the fact that within their scriptures, remains a large amount of authentic material. In spite of their deviation, difference and error in their practices, etc., their scriptures still contain the true version of the message.
Recently we had a number of Christians who converted to Islam saying, “I became Muslim by reading the Bible itself.” Thus, this is a special concession given, and you will find that the Qur’an mentions in many places that the closest people to the Muslims are the Christians. This closeness is actually the fact that the Jews are closer in terms of the various legal terms, etc., whether it is in the similarity of food laws or that of teaching. However, the Qur’an says that the Christians are the closest because they were following the last messenger before the Prophet (ﷺ). Although the Jews remained in accordance and maintained the law, by rejecting Jesus they blinded themselves. This made it much more difficult for them to accept the truth. Generally, for every Jew that accepted Islam, one will find 1000 Christians.
Imam al-Tabari said, commenting on this verse:
“…and chaste women from those who were given the Scripture (Jews and Christians) before your time” this means, free woman from among those who were given the Scripture, i.e., the Jews and Christians who followed the Tawraat (Torah) and Injeel (Gospel). “Before your time” O believers in Muhammad, from among the Arabs and all of mankind, you may marry them also “when you have given their due Mahr” i.e., when you give the mahr or dowry to those whom you marry from among your (Muslim) chaste women or their chaste women.” 
It is not permissible for a Muslim man to marry a Magian (Zoroastrian), Hindu, Communist or idol-worshipping woman, etc. The evidence for that is the verse in which Allaah says, (interpretation of the meaning):
“And do not marry Al-Mushrikaat (idolatresses) till they believe (worship Allaah Alone). And indeed a slave woman who believes, is better than a (free) Mushrikah (idolatress), even though she pleases you…” 
And Allah knows best.
 Surah Al-Ma’idah, 5:5
 Tafseer al-Tabari, 6/104
 Surah al-Baqarah, 2:221< Back to Questions