The God of my mercy shall prevent me - Or rather, “My God - his mercy shall prevent me.” This is in accordance with the present reading of the Hebrew text, and is probably correct. The psalmist looks to God as his God, and then the feeling at once springs up that his mercy - favor - his loving-kindness - “would” “prevent” him. On the word “prevent” see the notes at Psalms 21:3; compare Psalms 17:13; Psalms 18:5. The meaning here is, that God would “go before him,” or would “anticipate” his necessities.
God shall let me see my desire upon mine enemies - That is, He will let me see them discomfited, and disappointed in their plans. This is equivalent to saying that God would give him the victory, or would not suffer them to triumph over him. See the notes at Psalms 54:7.