Why can a Sikh girl not marry a Muslim, and is it permissible for them to marry?

The marriage of a Muslim man to the woman asking the question is not forbidden if she embraces Islam. Her closest Muslim relatives should arrange her marriage. If there are none, then she should be married by a Muslim judge or the head of the Muslim community. Islamic Sharia prohibits the marriage of a Muslim woman to a non-Muslim man, but it permits a Muslim man to marry a woman from the People of the Book, and no one else. This is because the man's influence on the wife is less significant, and because the disbelief of the People of the Book is less severe, and because they are followers of a previous revelation. Allah says: (And do not marry polytheistic women until they believe. And a believing slave woman is better than a polytheistic woman, even though she might please you. And do not marry polytheistic men [to your women] until they believe. And a believing slave man is better than a polytheistic man, even though he might please you. Those invite to the Fire, but Allah invites to Paradise and forgiveness by His permission. And He makes clear His verses to the people that perhaps they may remember) Al-Baqarah/221. It is not permissible for a Muslim man to marry a Sikh woman unless she embraces Islam. We advise utilizing this matter as an incentive for her to embrace Islam.