Repentance is a turning away from sin and toward God. It is the realization that our way is lacking and His is perfect. The author of Psalm 19 is saying that both creation and the law preach God in different ways and intend on leading us toward himself.
Saved by Grace Alone
Our righteousness is not our own. No measure of good behavior or abstention can make any sort of dent in the work that was already done.
The bathing suit argument
Legalism puts words in God's mouth and makes outward things higher than the matters of the heart.