He shall send from heaven - That is, from himself; or, he will interpose to save me. The psalmist does not say “how” he expected this interposition - whether by an angel, by a miracle, by tempest or storm, but he felt that help was to come from God alone, and he was sure that it would come.
And save me from the reproach ... - This would be more correctly rendered, “He shall save me; he shall reproach him that would swallow me up.” So it is rendered in the margin. On the word rendered “would swallow me up,” see the notes at Psalms 56:1. The idea here is, that God would “rebuke” or “reproach,” to wit, by overthrowing him that sought to devour or destroy him. God had interposed formerly in his behalf Psalms 57:2, and he felt assured that he would do it again.
Selah - This seems here to be a mere musical pause. It has no connection with the sense. See the notes at Psalms 3:2.
God shall send forth his mercy - In saving me. He will “manifest” his mercy.
And his truth - His fidelity to his promise; his faithfulness to those who put their trust in him. He will show himself “true” to all the promises which he has made. Compare Psalms 40:11.