I myself believe David alone watching the sheep on the Sabbath in his youth, his worship service could contend with any service today. The shepherd was consider the low, because you couldn't go to the sabbath service. I wonder how his service was by himself?
David had a very unique relationship with the Lord. And the Lord loved David; Just read the psalms & think about all he (David) brought before the Lord. There musta been great peace & joy in that communion. Praise God!