The phrase, “Lord, by thy power shall the king rejoice, and in thy salvation shall he greatly rejoice,” can be seen as David addressing the Lord Christ, who is, as Paul states, the power of God, saying: “...Christ the power of God, and the wisdom of God.” He is also the Savior, as noted by the Evangelist: “He shall save his people.” Accordingly, we can interpret that the king rejoices in the salvation You have accomplished.
This allows for a dual interpretation of the other phrases, some referring to the Father and others to the Son. David indeed rejoiced, for even after death, he beheld the mystery of God’s incarnation. If he perceived the future with the soul's sight in his physical body, he saw it even more clearly upon death, when he shed his earthly form. The ‘desire of the heart’ signifies David's longing to witness the Savior’s incarnation, of which he only glimpsed a shadow. The ‘desire of the mouth’ denotes his aspiration to continually praise God. Indeed, he perpetually sings through the mouths of Christians, who daily chant the sacred psalms.
He pleaded for life and was granted it, for when he anticipated death from his foes, he overcame them solely through prayer. The great glory of David was Thy salvation, which came from You. He was truly honored, as from his lineage arose our Salvation, the Sovereign and glorious Christ. “Thou wilt make him glad with joy before Thy face,” meaning You will bring him joy through Thy Son; for the Son is the visible manifestation of the Father, as He affirmed, “He that hath seen Me hath seen the Father.”
The adversaries of God can be seen as those who despise Christ—the Jews—who are cursed and destined for the suffering that follows, with their entire lineage laid waste by the Romans, the crucifiers of the Lord. Only those who had been dispersed into foreign lands managed to escape this destruction. “Thou shalt set them as a burning furnace in the time of thy face,” referring to Thy Son as noted earlier. When Christ took on flesh and declared, “Therefore the kingdom of God is taken away from you,” these tragedies began to befall them. “Upon the remnant of them,” meaning the Hebrews who embraced You, the Son. “Thou wilt prepare,” signifying adornments—You will honor their lineage. The Hebrews experienced the honor of being the ancestors of the apostles, despite being collectively despised.
At times, this Psalm suits another of our righteous kings in addition to the previous one concerning the nations. Theodoret expresses that God elevates without being humiliated, revealing His essence rather than what He lacks. Thus it is fitting to declare: “Be exalted, O Lord, by Thy power,” for Thy majesty is displayed through unsurpassable might, which we shall perpetually sing of and glorify by recounting Thy wonders. In the end times, when they are called, their boldness shall also be granted, for when, according to Paul, the fullness of the Gentiles enters, then Israel shall be saved.