His glory is great in thy salvation. David' s glory exceeds that of all other living men, through the "salvation" which God vouchsafes him. That salvation is partly temporal, consisting in deliverance from his foes; partly of an unearthly and spiritual character, arising out of his relationship to the coming Messiah.
It is from the latter point of view, rather than the former, that it is said, Honour and majesty hast thou laid upon him.