Continuing the exhortation style begun in 4:8-20, Paul dives further into what the gospel looks like in real life. He starts with the contrast of slavery and freedom that the previous chapter developed. Getting circumcised was the entrance rite into the Jewish community, and with it came the obligation to keep the entire law. Choosing that path is rejecting Jesus (v4)!
Verses 1 & 13 both touch on the same theme: we’re called to freedom from the law. Freedom can be abused, Paul admits, and we can read more about this in 1 Cor. 6:12, 10:23, and Rom. 14:1-13. The Judaizers are creating the opposite problem, though, and destroying a Christian’s freedom. The correct balance between these extremes are summed by verses 6 & 14: faith expressed through love (see Lev. 19:18 and Matt. 22:39).
Then Paul takes us into the spiritual depths of this subject, contrasting the works of the Spirit with the works of “the flesh,” or the sinful nature. Similar to Romans 8, Paul describes what life in the Holy Spirit ought to look like. Perhaps most famously, he gives a list of “fruits of the Spirit,” naming several good virtues that come from the indwelling of the Holy Spirit.