Psalms 21:1

The king shall joy in thy strength, O Lord,.... 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 withstand temptations and sin; and in keeping them safe to the end; in supporting them under all their trials, and in carrying on and finishing the work of faith upon their souls; all which is matter of joy to Christ;

and in thy salvation how greatly shall he rejoice? meaning either his own salvation by the Lord, from all his sorrows and troubles, and out of the hands of all enemies, being in the presence of God, where is fulness of joy, Psalms 16:9; or else the salvation of his people by him, which Jehovah appointed them to, secured for them in the covenant of grace, sent Christ to work out for them, applies by his Spirit, and at last puts into the full possession of: Christ rejoices at the effectual calling and conversion of his people, when salvation is brought near unto them; and especially at their glorification, when they shall be in the full enjoyment of it; then will they be his joy, and crown of rejoicing: this is the joy that was set before him, which made him go so cheerfully through his sufferings and death for them,

Hebrews 12:2; the reasons of this joy are, because of the great love he bears to them; the interest and property he has in them; his undertakings for them, as their surety, to bring them safe to glory; his purchase of them by his blood; his intercession for them, that they might be with him to behold his glory; and, last of all, because of his Father's glory, his own glory, and the glory of the blessed Spirit, which are concerned in the salvation of these persons.