The psalmist is a worship leader, he invites fellow servants to “Come, bless the Lord.” He invites them to lift up “holy hands”, as a public declaration, symbolic to their spiritual condition of being set apart. To “bless” the Lord, which we recently learned from Psalm 1 and Jesus’ sermon on the mount to mean to “be happy”. To make God happy.
What makes God happy? It is to be reunited with the people he cares so much for. To see His children with holy hands, holy hearts, living holy lives. To see that His great sacrifice on the cross was not in vain. To see his children as one.