The acts of the flesh are obvious (literally The works of the flesh are): Emphasizing law-keeping and sinful actions comes from trying to live without God's Spirit.
obvious: All people have a basic sense of right and wrong (see Romans 1:32; 2:14–15; 1 Corinthians 5:1). But some people still choose to do wrong anyway (Romans 1:18–21).
The list of acts of the flesh starts with sexual immorality. In contrast, the list of Christian virtues starts with love (Galatians 5:22). Various kinds of sexual misconduct were common (see Romans 1:24–27; 1 Corinthians 5:1; 6:15–18; 2 Corinthians 12:21; 2 Peter 3:10, 18). In ancient pagan religions, people engaged in sexual activities as part of their worship of fertility gods and goddesses (see Revelation 2:14, 20).
When people sin, they become spiritually unclean and cannot have fellowship with God, who is perfectly pure and holy (see Matthew 23:27; Romans 6:19; 2 Corinthians 12:21; Ephesians 5:3; Colossians 3:5; 1 Thessalonians 4:7).