1 Cor. 7:1-16 Paul makes recommendations for a happy marriage between two believers: “each man should have his own wife, and each woman should have her own husband” (1 Corinthians 7:2). They should share fully with each other as a married couple. Paul adds a command from the Lord Jesus: “A wife should not leave her husband… Also the husband should not divorce his wife.” (1 Corinthians 7:10-11).
A happy marriage between two believers - 40 years on.
1 Cor. 7:17-24 In an age when slavery was commonplace, Paul says, “Each one of you should stay the way you were when God called you. If you were a slave when God called you, do not let that bother you. But if you can be free, then make good use of your freedom” (1 Corinthians 7:20-21).
1 Cor. 7:25-40 Paul gives his own personal opinion that those who are unmarried should remain so. Widows may re-marry – but believers should only marry another Christian.
Paul himself was unmarried; but Peter and James – the leaders of the church in Jerusalem – both had Christian wives (see 1 Corinthians 9:5).