Like Ps. 20, its companion, Ps. 21, is a liturgical psalm intended for use in the public worship service. It is a psalm of thanksgiving on the success of the campaign for which the preceding psalm was the supplication. It has three parts: direct thanksgiving to God on behalf of the king (vs. 1-7), an address to the king (vs. 8-12), and a final ejaculation of praise (v. 13). The psalm presents a splendid picture of the king: dignified, glorious, invincible in God’s might.
On the superscription see pp. 616, 627.
In thy strength.
The chariots and horses were powerless against God’s strength (see Ps. 20:7). The reversing of the order of ideas in the parallelism is a favorite rhetorical device: “joy ... strength”; “salvation ... rejoice.” God’s salvation had previously been anticipated (Ps. 20:5, 6, 9). Now it is realized. Ancient Jewish tradition regarded the psalm as Messianic, as is shown by the free translation of the Targum: “O Lord, in thy strength king Messiah shall rejoice.”
The king.
Verses 1-7 express the gratitude of the congregation for the victory God has given the king. It is always becoming to make public recognition of answered prayer.
The king is probably David. Here the expression ledawid, “by David,” or “for David” (see p. 616), should probably be translated “concerning David.”