My defense is of God - The meaning here is, that God was his protector, and that in his troubles he confided in him. The original word here, as in Psalms 3:3, note; Psalms 5:12, note; is “shield.” See the notes at thoses verses.
Which saveth the upright in heart - whom he that searches the heart Psalms 7:9 sees to be upright; or to be sincere, truthful, just. The writer says that it is a characteristic of God that he saves or protects all such; and, conscious of his innocence of the charges against himself, he here appeals to him on that ground, and confides in his protection because he sees that in this respect he was blameless.