The Schizophrenic Psalmist?

When one takes to reading the psalms consecutively, it is not long before certain themes are seen developing. In Psalm one we find that there are two types of people, the righteous and the wicked, the blessed and the cursed. Psalm two tells us of God's king, the one who will judge the nations with a rod of iron. It is not long until we see that this righteous king and the righteous people of God suffer at the hands of the wicked and cry out to God "How long, O Lord?" though the righteous one trusts in the Lord while the wicked trusts in himself. The psalmist tells us that the Lord knows the way of the righteous, he loves the righteous, but hates all evildoers. This tension points us forward to a consummation, when the rigtheous will finally be vindicated, finally and fully delivered, and the wicked will be justly condemned.

We can understand these polarizing themes of blessing and cursing, the righteous and the unrighteous, salvation and judgment. What is confusing is the psalmist's own words about himself. David, God's king who writes most (if not all) of these early psalms, is confident of God's favor. He trusts in the Lord. He is bold as a lion in declaring that the Judge of all the earth will do right. He is also confident that he is the Lord's holy one, blameless, and righteous. The words of psalm 18 are almost hard to read:

20 The Lord dealt with me according to my righteousness;
according to the cleanness of my hands he rewarded me.
21 For I have kept the ways of the Lord,
and have not wickedly departed from my God.
22 For all his rules were before me,
and his statutes I did not put away from me.
23 I was blameless before him,
and I kept myself from my guilt.
24 So the Lord has rewarded me according to my righteousness,
according to the cleanness of my hands in his sight.

 
I say that these words are hard to read because of the man who pens them down. David says all of this but we also find him confessing his own sin to the Lord, being at times in agony over his transgressions. We know from his biography that David is an adulterer and a murderer. Which is it, is he righteous or sinful? Does the psalmist of Israel suffer from schizophrenia? Do the psalms give us insight into the mind of a crazy and confused man? Do his words that come later in Psalm 51 negate everything in the earlier part of the psalter? Doesn't he realize that he is calling down judgment on himself when he calls for God to make the unrighteous bear their own guilt? He declares a universal depravity, that the Lord looks down from Heaven and finds none who are righteous, none who seek after God and yet does David have the gall to believe that the Lord will not destroy him as well?
How is this dilemma solved? We must remember that David could say these things because of the God he hoped in (Psalm 5:7, 11) and we must also see how the apostles interpreted the psalms in the New Testament, that is, in light of Christ. The truth is that David was only a shadow of the true King who was to come. Any righteousness that we see in David is only a shadow of the righteousness brought by the true King. This King would be truly righteous, he would be the true Israel who kept perfectly the law of the Lord and fulfilled all of its demands. This King would earn a righteousness for his people so that they may stand in the Day of Judgment and be bold like David though they are sinners like David. Christ would truly suffer at the hands of wicked men as the servant of God being truly forsaken of the Father while David only felt that God had abandoned him, but he would be raised from the dead as David had said (Psalm 16:10).
Who is this one who may ascend the hill of the Lord and stand in his holy place? It is only he who has clean hands and a pure heart who will receive blessing and righteousness from the Lord. As he ascends the hill of the Lord the gates and doors are commanded to be lifted that this righteous king may come in. Who does David say this king is? It is not himself, it is the King of Glory, the Lord of hosts, strong and mighty (Psalm 24), and he alone leads his people into the presence of God. Remember the Christ of the Psalms.