This psalm was written about Doeg the Edomite, who had betrayed Ahimelech and David and then killed God's priests (see 1Sa 21:7; 1Sa 22:9-23). Doeg thought he was a great warrior—even boasting about his deed. In reality, his deed was evil, an offense to God. It is easy to mistake "accomplishment" for goodness. Just because something is done well or thoroughly doesn't mean it is good (for example, someone may be a great gambler or a skillful liar). Measure all you do by the rule of God's Word, not by how proficiently you do it.
Psalms 52:8
With God by his side, David compared himself to an olive tree, thriving in the house of God. Not only is an olive tree a thriving tree, it is one of the longest-living trees. David was contrasting God's eternal protection of his faithful servants with the sudden destruction of the wicked (Psa 52:5-7).
