Worship is about the worshipper ascribing worth to what is worshipped.
We all worship something, in our hearts we all put ultimate worth in something. But the worship that the Bible describes is not about merely singing hymns at church every Sunday. The Bible describes worship as a way of life, an attitude towards life that places God at the center. Because only God is ultimately worthy to be worshipped and sought after. David describes a deep spiritual and physical longing for his God because nothing else seems to fill his emptiness, and his desperate cry is for wholeness.