The book of Psalms opens with a description of the righteous man. The righteous man follows the law of God, meditating upon it always. He is like the undying tree of life in the Garden of Eden. This man is Christ, who through his resurrection from the dead restores us from death to the garden. This psalm is placed first to let the reader of the Psalms know that the entire book is a series of praises of Christ.
Blessed is the man who walks not in the counsel of the wicked, nor stands in the way of sinners, nor sits in the seat of scoffers; but his delight is in the law of the Lord, and on his law he meditates day and night. He is like a tree planted by streams of water, that yields its fruit in its season, and its leaf does not wither. In all that he does, he prospers.
Christ is risen from the dead,
By death trampling down on death,
And to those in the tomb,
He has granted life!