There is none greater in this house than I; neither hath he kept back any thing from me but thee, because thou art his wife: how then can I do this great wickedness, and sin against {g} God?

(g) The fear of God preserved him against her continual temptations.

Wesley's Notes

39:9 How can I sin against God - Not only how shall I do it and sin against my master, my mistress, myself, my own body and soul, but against God? - Gracious souls look upon this as the worst thing in sin, that it is against God, against his nature and his dominion, against his love and his design. They that love God, for this reason hate sin.

Jamieson-Fausset-Brown Bible Commentary

9. How then can I do this great wickedness, and sin against God?-This remonstrance, when all inferior arguments had failed, embodied the true principle of moral purity-a principle always sufficient where it exists, and alone sufficient.

Matthew Henry's Concise Commentary

39:7-12 Beauty either in men or women, often proves a snare both to themselves and others. This forbids pride in it, and requires constant watchfulness against the temptation that attends it. We have great need to make a covenant with our eyes, lest the eyes infect the heart. When lust has got power, decency, and reputation, and conscience, are all sacrificed. Potiphar's wife showed that her heart was fully set to do evil. Satan, when he found he could not overcome Joseph with the troubles and the frowns of the world, for in them he still held fast his principle, assaulted him with pleasures, which have ruined more than the former. But Joseph, by the grace of God, was enabled to resist and overcome this temptation; and his escape was as great an instance of the Divine power, as the deliverance of the three children out of the fiery furnace. This sin was one which might most easily beset him. The tempter was his mistress, one whose favour would help him forward; and it was at his utmost peril if he slighted her, and made her his enemy. The time and place favoured the temptation. To all this was added frequent, constant urging. The almighty grace of God enabled Joseph to overcome this assault of the enemy. He urges what he owed both to God and his master. We are bound in honour, as well as justice and gratitude, not in any thing to wrong those who place trust in us, how secretly soever it may be done. He would not offend his God. Three arguments Joseph urges upon himself. 1. He considers who he was that was tempted. One in covenant with God, who professed religion and relation to him. 2. What the sin was to which he was tempted. Others might look upon it as a small matter; but Joseph did not so think of it. Call sin by its own name, and never lessen it. Let sins of this nature always be looked upon as great wickedness, as exceedingly sinful. 3. Against whom he was tempted to sin, against God. Sin is against God, against his nature and his dominion, against his love and his design. Those that love God, for this reason hate sin. The grace of God enabled Joseph to overcome the temptation, by avoiding the temper. He would not stay to parley with the temptation, but fled from it, as escaping for his life. If we mean not to do iniquity, let us flee as a bird from the snare, and as a roe from the hunter.