Translation:

221. Do not marry unbelieving women (idolaters) until they believe; a slave woman who believes is better than an unbelieving woman even though she allure you. Nor marry (your girls) to unbelievers until they believe: a man slave who believes is better than un unbeliever even though he allure you. Unbelievers do (but) beckon you to the fire. But Allah beckons by His grace to the Garden (of Bliss) and forgiveness and makes His Signs clear to mankind: that they may celebrate His praise.

Notes (Tafseer)

246. Marriage is a most intimate communion, and the mystery of sex finds its highest fulfilment when intimate spiritual harmony is combined with the physical link. If religion is at all a real influence in life to both parties or to either party, a difference in this vital matter must affect the lives of both more profoundly than differences of birth, race, language, or position in life. It is therefore only right that the parties to be married should have the same spiritual outlook. If two person love each other, their outlook in the highest things of life must be the same. Note that religion is not here a mere label or a matter of custom or birth. The two persons may have been born in different religions, but if, by their mutual influence, they come to see the truth in the same way, they must openly accept the same rites and the same social brotherhood. Otherwise the position will become impossible individually and socially.