“Bless the Lord, O my soul, and all that is within me, bless his holy name!” (Psalm 103:1)
The psalm begins and ends with the psalmist preaching to his soul to bless the Lord—and preaching to the angels and the hosts of heaven and the works of God’s hands. The psalm is overwhelmingly focused on blessing the Lord. What does it mean to bless the Lord? It means to speak well of his greatness and goodness. What David is doing in the first and last verses of this psalm, when he says, “Bless the Lord, O my soul,” is saying that speaking about God’s goodness and greatness must come from the soul. Blessing God with the mouth without the soul would be hypocrisy. Jesus said, “This people honors me with their lips, but their heart is far from me” (Matthew 15:8). David knows that danger, and he is preaching to himself that it not happen.
Come, soul, look at the greatness and goodness of God. Join my mouth, and let us bless the Lord with our whole being. (Tozer)