It's difficult to get a group, even a very good group, to move ahead in a united decision. Different heads have different thoughts, different tastes, and different plans of attack. It's not easy to move as one.
Or look at the state of marriage in our society. Nowhere is unity more important and yet, frequently, more elusive. To take two minds and hearts and make them breathe as one requires no small miracle. A marriage licence is needed to help cement a covenant because romance alone won't do the job. Unity is a life-long task and commitment.
But the Psalmist zeros in on the place where unity is the most difficult of all - and the most crucial to achieve: "Bless the Lord, O my soul, and all that is within me, bless His holy Name." All of you - everything within you - has to make the same decision to honor the Lord. There has to be inward unanimity in the commitment to bless His Name.