ANSWER: There is no human law against it, nor any prohibition in the Decalogue, but an inspired apostle forbids it, "Be not unequally yoked with unbelievers" (II Cor. 6:14-17). "The apostle," says Wesley, "speaks especially of marriage and gives three arguments against it in the context." Many a Christian has made a shipwreck by violating this prohibition, thinking that conversion would be effected by home missionary work. But instead of that the unbelieving husband often perverts the Christian wife by urging her to go with him to the theater, the dance, the card party, and the Sunday excursion. (2) We have always admired the refusal of Spurgeon to celebrate the marriage of any member of his church with an unbeliever, though I have not always followed his example. He illustrates the delusion of the expectation of conversion after marriage on this wise: "It is like one standing on a table trying to lift them up to his level. The one below will almost certainly pull the other down." History proves this. Professedly Christian parents, who prefer for their daughter a rich sinner to a poor saint will have much to answer for in the day of judgment, and. often in this life sorrows follow such a marriage in the shape of divorce, or wicked, sons-in-law or ungodly grandchildren.
— Steele's Answers pp. 189, 190.