The subject Paul is continuing is mixed-religion marriages: a Christian with a non-believer. He is given illustrations to show the basic concept applies to more than mixed-religion marriages. The basic concept is repeated a third time in verse 24, “Brothers, each man, as responsible to God, should remain in the situation God called him to.” This is also stated in verses 17 and 20. The illustration given in these verses is that of being a slave and a freeman.
If the person became a believer in Jesus when they are a slave, remain a slave and be content with that (21). The short letter to Philemon addresses a runaway slave, Onesimus, who became a believer in Jesus while Paul was in chains. Paul sent the runaway slave back to his owner, instructing him to accept the man as a believer, and consider releasing the man from slavery. (Philemon 1:12-16)
Of note, the advice here given is that if a chance to gain freedom is offered to the slave, they should take it. Improving the condition and circumstances of our lives is not wrong. What is wrong is not accepting and being content wherever God has placed me.
How can I be content in all and every situation? Know my place with Christ. Though slave to man, I am free in Christ. Though slave to no man, I am slave to Christ, and better because of it, for I was bought by Christ Jesus from slavery to sin and death with the blood of Christ, and so I am free to live as a slave to him. Far better to be a slave to Jesus than a man who believes he lives free, but is actually a slave to sin and death. Praise be to God. My eyes are opened.
