As you read through this particular part of the Bible there are three threads that become obvious.
The first begins in the first Psalm when we learn the character of the man who is blessed by God Psalm 1:1-3 and throughout the rest of the Psalms you see that those who were trying to be that kind of person, hopefully every Christian is striving with the help of the Holy Spirit to live up to this standard. You find there is a constant battle to be this kind of person. We see their failures and we learn of their cries for forgiveness. Create in me a clean heart oh God (Psalm 51:10) is one such cry. It is a constant source of encouragement to know that others have gone through similar experiences and know that we too can cry for forgiveness for our failures and find the spiritual caliber to praise the Lord.