The psalmist contemplates the wickedness of those who oppress the people of God and think in their hearts that He does not exist and does not see their wickedness. He calls upon God to remember their evil and to bring them into judgment for it.
We consider both the sternness and the kindness of our God - in judging the wicked and in saving His people. We see that we should not be too quick to seek God for the destruction of the lost - but rather that they would turn from their sins and live. This is a motivation to us to take out the Gospel and seek out those whom God has chosen to save.
Above all, we remember that our God is king and that He will protect us from all harm and bring all those to glory for whom Christ died.