Paul continues with his discussion of marriage by saying that we should all serve where we were called. We don’t need to change our position or situation in order to be useful for the Lord. We need to influence others where we are. If you can’t do much about being a slave, serve God while a slave. If you can get free, great (7:21), but don’t think you can’t serve because of your slavery. In fact, with God, we’re all in the same boat. Slaves are given freedom in Christ, and those who are free are called to be slaves (7:22). Think about that for a little bit!
Paul then goes back to marriage, and his understanding of the doctrine of immanency informs his words (7:29, 31). The idea of immanency (that Christ could return at any moment) leads him to state that you shouldn’t marry if you are currently single (whether a widow or dating). You have the opportunity to devote your life to God, so do it! However, we have to take into account what Paul has already said. He understands that it’s difficult for most to handle singleness. However, if you can, it gives you greater opportunities to serve the Lord (7:33-34).
Three quick notes.  There is a footnote in the online NET Bible at 7:36. “Past the bloom of youth” could also be “if his/her passions are too strong.” The word literally means “past the high point.” The reasoning could be that a man has waited so long to marry a woman that she is beyond any hope of finding someone else, so he marries her. The other option corresponds well with what Paul said earlier in 7:9 and is my preferred understanding.  Did you catch what Paul said about a widow remarrying? “She is free to marry anyone she wishes (only someone in the Lord)” (7:39). Here is a good rationale for the argument that Christians should marry Christians.  Paul’s words in 7:29-31 remind us that, even with our marriages and families, our priority is always God. Yes, we are called to take care of and love our families. But our greatest passion should be service to God. There is no time to waste!