The psalmist, David was richly blessed by God. He expressed his praise to the Lord for those blessings and related how his enemies, who were also the enemies of God had been destroyed by the righteous Judge. Those who are oppressed as they serve God can find a refuge in Him, but the wicked will find that hell is their place.
When one is being oppressed, it is easy to think that God has forgotten him. He may cry out in despair for deliverance to a God who seems to be hidden. David described many of the actions of the wicked. When they seem to prosper and avoid punishment, they forget that God the righteous judge will reward them according to their evil deeds. However, God does see and does execute righteous judgment to both the good and to the evil.