Great is the glory of the king through the salvation of the Lord. Also read Psalm 20:6 Now I know that the Lord saves his anointed; he will answer him from his holy heaven with the saving might of his right hand.
The Lord adorns him with brilliance and glory. Thus, the king is doing very well. But this is only due to the blessings (Psalm 21:3) of the Lord God. All power belongs to God. Every ruler owes power and knowledge to God, the King. That is what the poet confesses. And this poet could be the king himself whom this Psalm is about.
Here we also notice a messianic trait, if we look at Hebrews 2:9, for a little while was made lower than the angels, namely Jesus, crowned with glory and honour because of the suffering of death, so that by the grace of God he might taste death for everyone.
5 His glory is great through your salvation; splendor and majesty you bestow on him.