Wherefore he slew him also - The sin of Onan has generally been supposed to be self-pollution; but this is certainly a mistake; his crime was his refusal to raise up seed to his brother, and rather than do it, by the act mentioned above, he rendered himself incapable of it. We find from this history that long be fore the Mosaic law it was an established custom, probably founded on a Divine precept, that if a man died childless his brother was to take his wife, and the children produced by this second marriage were considered as the children of the first husband, and in consequence inherited his possessions.

And the thing which he did displeased the Lord,.... Being done out of envy to his brother, and through want of affection to the memory of his name; and it may be out of covetousness to get his estate into his own hands, and especially as it frustrated the end of such an usage of marrying a brother's wife; which appears to be according to the will of God, since it afterwards became a known law of his; and it was the more displeasing, as it was not only a check upon the multiplication of Abraham's seed as promised, but since the Messiah was to come from Judah. This was doing all to hinder it that lay in his power:

wherefore he slew him also; in like manner as he had slain his brother, Genesis 38:7.

And the thing which he did displeased the LORD: wherefore he slew him also.

displeased...: Heb. was evil in the eyes of the Lord

38:1-30 The profligate conduct of Judah and his family. - This chapter gives an account of Judah and his family, and such an account it is, that it seems a wonder that of all Jacob's sons, our Lord should spring out of Judah, Heb 7:14. But God will show that his choice is of grace and not of merit, and that Christ came into the world to save sinners, even the chief. Also, that the worthiness of Christ is of himself, and not from his ancestors. How little reason had the Jews, who were so called from this Judah, to boast as they did, Joh 8:41. What awful examples the Lord proclaims in his punishments, of his utter displeasure at sin! Let us seek grace from God to avoid every appearance of sin. And let that state of humbleness to which Jesus submitted, when he came to put away sin by the sacrifice of himself, in appointing such characters as those here recorded, to be his ancestors, endear the Redeemer to our hearts.