And do not marry polytheist women till they believe, and a believing slave girl is certainly better than a polytheist woman though she pleases you. And do not marry polytheist men till they believe, and a believing slave is certainly better than a polytheist man though he pleases you. Those invite (you) to the fire while Allah invites (you) to the garden and protective forgiveness through His order, and makes clear His signs for the human beings so that they may be mindful. (R 27)
“Polytheism is an unforgivable sin 4:48. If a Muslim marries a polytheist, the danger of adopting beliefs and practices of polytheism cannot be ruled out. It is a well-known fact that precaution is better than cure, therefore Muslims have been stopped from marrying polytheists. A believing slave (man or woman) who is normally considered low in the society is better than a polytheist even if he or she is pleasing because they invite towards hell whereas Allah (SWT) invites towards paradise. Allah (SWT) makes things clear for mankind so that they may be mindful and avoid things leading to hell.”