I believe that God set this psalm first because it functions as the foundation for he proper operation of the human soul. The psalm begins with a declaration of blessedness.
Blessed is the man that walketh not in the counsel of the ungodly, nor standeth in the way of sinners, nor sitteth in the seat of the scornful.This psalm indicates the difference in the souls of the one who does not walk with the iniquitous. This does not mean one should shun others. It indicates a close association. Some have noted a progression from walking, to standing, to sitting, indicating a gradual acceptance of the ways and thought processes of the wicked. This behavior leads to moral and psychological maladies.
But his delight is in the law of the LORD; and in his law doth he meditate day and night.In contrast to the disruptive life of the wicked, those who would live in peace and wholeness must appropriate the scriptures. "Meditate" does not indicate the eastern notion of transcendental meditation, the divestment of conscious thought in an attempt to perceive truth beyond the rational. Reading in the ancient near east was not done silently, but aloud. Meditation involved reading the text repeatedly. It means muttering God's word to oneself. The psychologically whole person lives with God's word running through his head.
The psalmist particularly emphasizes the scripture because in them, God reveals Himself. We know Him through them. Our relationship with God depends upon His revelation.
And he shall be like a tree planted by the rivers of water, that bringeth forth his fruit in his season; his leaf also shall not wither; and whatsoever he doeth shall prosper. The ungodly are not so: but are like the chaff which the wind driveth away.The notion of emotional and psychological stability seems attached to the modern world. While we probably ought not assume this psychological construct upon the text, even in that day, the readers would have appreciated the distinction between a planted tree and loose chaff. The one who roots himself in scripture anchors his soul to that which can never be moved. Though the winds that drive the chaff to desolation may blow against the planted tree, he will withstand them because of his roots.
Therefore the ungodly shall not stand in the judgment, nor sinners in the congregation of the righteous. For the LORD knoweth the way of the righteous: but the way of the ungodly shall perish.The psalm concludes with a description of the forensic consequences of the distinction between the righteous and the wicked. In the eschatological judgment, God will divide the two groups. You might be excused into thinking that God bases His judgment on the works of the respective groups. This interpretation cannot stand considering the final verse. It is not the merits of the people, but the knowledge of God. The relationship with God divides the wicked from the righteous. You might say that the first step in psychological wellness comes by knowing God.
Christian counseling seeks to address the wretched effects of the sin. I would never denigrate their valiant efforts. However, any treatment that does not begin with the necessity of regular repetitive study of God's word addresses the symptoms without healing the malady. True spiritual wellness comes from God, knowing Him through His word and living in ways that glorify Him. The first message of God's "anatomy of the soul" teaches us that God's word forms the most effective physic.