Psalms 57:3

He shall send from heaven There is no need to supply an object to the verb here. The object is introduced when the verb is repeated according to the characteristic peculiarity of this Psalm. For the meaning cp. Psalms 20:2, and perhaps Psalms 18:16, though see note there.

from the reproach&c. Better, (For) he that would swallow me up (or, crush me, Psalms 56:1, note) hath reproached. The object of the verb may be God, Whom the enemy blasphemes in denying His willingness to help His servant (Isaiah 37:23-24); or the Psalmist, whom he taunts with being deserted by his God (Psalms 42:10; Psalms 55:12). The rendering of A.V. marg., he reproacheth him that would swallow me up, is contrary to usage, for the word is never used of God rebuking men.

Selahhere is probably misplaced, cp. Psalms 55:19. In the LXX it follows Psalms 57:2.

God shall send forth&c. God's lovingkindness and truth(cp. Psalms 42:8; Psalms 43:3) are almost personified as "ministering spirits, sent forth to do service for the sake of them that shall inherit salvation." It is in virtue of the lovingkindness which is the foundation of His covenant, and of the faithfulness which is an inalienable attribute of His nature, that God will send help to His servant.