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.)

A man shall not take his father's wife - This is to be understood as referring to the case of a stepmother. A man in his old age may have married a young wife, and on his dying, his son by a former wife may desire to espouse her: this the law prohibits. It was probably on pretense of having broken this law, that Solomon put his brother Adonijah to death, because he had desired to have his father's concubine to wife, 1-Kings 2:13-25.

A man shall not (l) take his father's wife, nor discover his father's skirt.
(l) He shall not lie with his stepmother, meaning by this all other variations forbidden in (Leviticus. 18:1-30).

A man shall not take his father's wife,.... Not marry her, whether his own mother, or a stepmother; or even, as Aben Ezra thinks, anyone that was deflowered by his father. Jarchi interprets it of his father's brother's wife, which he was obliged to marry by virtue of the law in Deuteronomy 25:5.
nor discover his father's skirt; or lie with her his father had thrown his skirt over, or married; and which being the first, is mentioned here as a sample to all the rest forbidden Leviticus 18:7 or, as Bishop Patrick expresses it, is a "short memorandum", to make them careful to observe all the other laws respecting incestuous marriages and copulations there delivered.

(or Deuteronomy 23:1) This verse, in which the prohibition of incest is renewed by a repetition of the first provision in the earlier law (Leviticus 18:7-8), is no doubt much better adapted to form the close of the laws of chastity and marriage, than the introduction to the laws which follow concerning the right of citizenship in the congregation of the Lord.

Take - To wife. So this respects the state, and the next branch speaks of the act only.