Psalms 21:1

“The king shall joy in thy strength, O Lord, etc.] Either in that strength which is in Jehovah himself, in whom is everlasting strength; and which is seen in the works of creation and providence, and is the same in Christ himself, as he is the mighty God; or else in the strength which Jehovah communicated to Christ as man, whereby he was strengthened in his human nature to go through and complete the work of man’s redemption; or in the strength which the Lord puts forth, and the power which he exerts towards and upon his people, in conversion; which is the produce of the exceeding greatness of his power; and in strengthening them, from time to time, to exercise grace, discharge duty, and…”

“The pious are led by the Psalmist to celebrate God's favor to the king in the already conferred and in prospective victories. The doxology added may relate to both Psalms; the preceding of petition, chiefly this of thanksgiving, ascribing honor to God for His display of grace and power to His Church in all ages, not only under David, but also under his last greatest successor, "the King of the Jews." (Psa 21:1-13) thy strength . . . thy salvation--as supplied by Thee.”

“Ps 21 God’s people thank him for giving victory to the king.”

“The king: Psa 2:6, Psa 20:6, Psa 20:9, Psa 63:11, Psa 72:1, Psa 72:2; Isa 9:6, Isa 9:7; Mat 2:2 joy: Psa 28:7, Psa 62:7, Psa 95:1, Psa 99:4 in thy: Psa 20:5, Psa 71:17-24, Psa 118:14, Psa 118:15; Heb 12:2 Psalms 21:2”

“(Heb.: 21:2-3) The Psalm begins with thanksgiving for the bodily and spiritual blessings which Jahve has bestowed and still continues to bestow upon the king, in answer to his prayer. This occupies the three opening tetrastichs, of which these verses form the first. עז (whence עזּך, as in Psa 74:13, together with עזּך, Psa 63:3, and frequently) is the power that has been made manifest in the king, which has turned away his affliction; ישׁוּעה is the help from above which has freed him out of his distress. The יגיל, which follows the מה of the exclamation, is naturally shortened by the Kerמ into יגל (with the retreat of the tone); cf. on the contrary Pro 20:24, where מה is interrogative and,…”