Deuteronomy 22

30. A man shall not take his father's wife. Since Moses does not here refer to any other kinds of incest, but speaks only of that with a step-mother, it is probable that, what he had more fully set forth before he here briefly recalled to the minds of the Israelites under a single head. At any rate, the prohibition of one offense does not open the gate to other abominations. The expression which he adds, "nor discover his father's skirt," is as much as to say, that the father is exposed to shame when the step-son has; no regard to decency, and goes in to his step-mother. Perhaps he alludes to the sin of Ham, who betrayed his ungodliness by exposing the shame of his father. (Genesis 9:22.)