Keep back = restrain or hold back; as the motions of the heavenly bodies are controlled. First occurrence Gen_20:6; Gen_22:12, Gen_22:16; Gen_39:9. Compare 1Sa_25:39, &c.
from presumptuous sins. Figure of speech Hypallage.App-6. Hebrew keep back presumptuous [men] from me.
have dominion over = rule, as the sun and moon rule the day and night (Gen_1:18. Psa_136:8, Psa_136:9).