Psalm 1 surely is intentionally placed at the beginning as a prologue to set the tone for the entire collection of hymns. It announces that the primary agenda for Israel's life of worship is obedience, to order and conduct all of life in accordance with God's purpose and ordering of the creation. The fundamental contrast in this psalm and all of Israel's faith is a moral distinction between righteous and wicked, innocent and guilty; those who conform to God's purpose and those who ignore those purposes and disrupt the order. Human life is not mocked or trivialized. How it is lived is decisive.
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Psalm 1 is understood as a doorway to the whole Psalter. The book presents us with two ways: the way of the righteous and the way of the wicked. These two ways are in opposition throughout the whole Psalter.
1 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;