“Bless” means essentially to say or do good things to someone; as a result both the one who is blessed and one who gives a blessing normally feel better. This is how it usually works in human interaction. One can only imagine how wonderful life would be when people experience constant interactive, reciprocal blessings.
A believer’s relationship with God is similar except that God by nature doesn’t “feel better,” for He does not change and He cannot be improved; although He is pleased with faith in His Son and He is grieved with sin. In life we are continually blessing God and He is always blessing us. In worship, as in this Psalm, we bless the Lord and the Lord blesses us. We feel better.
Worship is like a doorway that opens out into the power and love behind the world. The One who made the heaven and the earth blesses the worshiper out of Zion, the church, the place of His Presence on earth. We receive the Gospel blessing in faith, and in turn, bless the Lord in an unending cycle of well-being. “Bless the Lord; the Lord bless you.”