It is very dangerous for a Christian to marry someone who has not made a heart and life commitment to Jesus Christ as Savior and Lord.
To be ready for marriage spiritually means, first of all, that both individuals have accepted Christ and eagerly intend to make Christ the Head of their home. To consider marriage without the possibility of spiritual agreement is to invite argument and unhappiness into the future household.
Mr. Graham has said, "I would not guarantee that with becoming a Christian, the whole problem of marriage and the home is automatically solved. But I do say that complete fulfillment in marriage can never be realized outside of the life of Christ. ... I would advise every couple planning to establish a home to first come to a complete agreement on their religious faith." Amos 3:3 states: "Can two walk together, except they be agreed?"
God ordained marriage to be a "perfect triangle" God, you, and your spouse. The closer each marriage partner lives to God, the closer each will live to the other. Such closeness is impossible when one spouse does not have a personal relationship with God.
This is the reason the Bible says we should not be unequally yoked; read 2 Corinthians 6:14-15. The apostle Paul applies this principle in the case of widows when he writes, "But if her husband dies, she is free to marry anyone she wishes, but he must belong to the Lord" (1 Corinthians 7:39b).