Listen to the words of J.C. Ryle as he counsels single Christians on the issue of considering marrying an unbeliever:
“This principle here laid down ought to be carefully remembered by all unmarried Christians in the choice of husband or wife. I fear it is too often entirely forgotten. Too many seem to think of everything except religion in choosing a partner for life, or to suppose that it will come somehow as a matter of course. Yet when a praying, Bible-reading, God-fearing, Christ-loving, Sabbath-keeping Christian marries a person who takes no interest whatever in serious religion, what can the result be but injury to the Christian, or immense unhappiness? Health is not infectious, but disease is. As a general rule, in such cases, the good go down to the level of the bad, and the bad do not come up to the level of the good. The subject is a delicate one, and I do not care to dwell upon it. But this I say confidently to every unmarried Christian man or woman,— if you love your soul, if you do not want to fall away and backslide, if you do not want to destroy your own peace and comfort for life, resolve never to marry any person who is not a thorough Christian, whatever the resolution may cost you. You had better die than marry an unbeliever. Stand to this resolution, and let no one ever persuade you out of it. Depart from this resolution, and you will find it almost impossible to ‘come out and be separate.’ You will find you have tied a millstone round your own neck in running the race towards heaven; and, if saved at last, it will be ‘so as by fire’ (1 Cor 3:15)” (pp. 283-84).