Albert Barnes Commentary Psalms 56:9

"Then shall mine enemies turn back in the day that I call: This I know, that God is for me." — Psalms 56:9 (ASV)

When I cry unto thee - This expresses strong confidence in prayer. The psalmist felt that he had only to cry to God to secure the overthrow of his enemies. God had all power, and his power would be put forth in answer to prayer.

Then shall mine enemies turn back - Then they will cease to pursue and persecute me. He did not doubt that this would be the ultimate result - that this blessing would be conferred, though it might be delayed, and though his faith and patience might be greatly tried.

For God is for me - He is on my side; and he is with me in my wanderings. Compare the notes at Romans 8:31.