Reefs are large rocks that are very close to the surface of water in the sea. Because sailors cannot see them, they are very dangerous. Ships can easily be destroyed if they hit these rocks. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Possible meanings are that these people are like 1) trees from which people expect to harvest fruit, but they have none, or 2) trees that never bear fruit. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Like trees that have been completely pulled out of the ground by their roots, the ungodly people have been separated from God, who is the source of life. (See: [[rc://en/ta/man/translate/figs-metaphor]])
As the sea's waves are blown by a strong wind, so the ungodly people are easily moved in many directions. (See: [[rc://en/ta/man/translate/figs-metaphor]])
As wind causes wild waves to stir up dirty foam—so these men, through their false teaching and actions, shame themselves. AT: "and just as waves bring up foam and dirt, these men pollute others with their shame" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Those who studied the stars in ancient times noticed that what we call planets do not move the way that stars do. AT: "disorderly stars" or "moving stars" (See: [[rc://en/ta/man/translate/figs-metaphor]])