Here is, 1. Judah's foolish friendship with a Canaanite-man. He went down from his brethren, and withdrew for a time from their society and his father's family, and got to be intimately acquainted with one Hirah, an Adullamite, Gen 38:1. It is computed that he was now not much above fifteen or sixteen years of age, an easy prey to the tempter. Note, When young people that have been well educated begin to change their company, they will soon change their manners, and lose their good education. Those that go down from their brethren, that despise and forsake the society of the seed of Israel, and pick up Canaanites for their companions, are going down the hill apace. It is of great consequence to young people to choose proper associates; for these they will imitate, study to recommend themselves to, and, by their opinion of them, value themselves: an error in this choice is often fatal. 2. His foolish marriage with a Canaanite-woman, a match made, not by his father, who, it should seem, was not consulted, but by his new friend Hirah, Gen 38:2. Many have been drawn into marriages scandalous and pernicious to themselves and their families by keeping bad company, and growing familiar with bad people: one wicked league entangles men in another. Let young people be admonished by this to take their good parents for their best friends, and to be advised by them, and not by flatterers, who wheedle them, to make a prey of them. 3. His children by this Canaanite, and his disposal of them. Three sons he had by her, Er, Onan, and Shelah. It is probable that she embraced the worship of the God of Israel, at least in profession, but, for aught that appears, there was little of the fear of God in the family. Judah married too young, and very rashly; he also married his sons too young, when they had neither wit nor grace to govern themselves, and the consequences were very bad. (1.) His first-born, Er, was notoriously wicked; he was so in the sight of the Lord, that is, in defiance of God and his law; or, if perhaps he was not wicked in the sight of God, to whom all men's wickedness is open; and what came of it? Why, God cut him off presently (Gen 38:7): The Lord slew him. Note, Sometimes God makes quick work with sinners, and takes them away in his wrath, when they are but just setting out in a wicked course of life. (2.) The next son, Onan, was, according to the ancient usage, married to the widow, to preserve the name of his deceased brother that died childless. Though God had taken away his life for his wickedness, yet they were solicitous to preserve his memory; and their disappointment therein, through Onan's sin, was a further punishment of his wickedness. The custom of marrying the brother's widow was afterwards made one of the laws of Moses, Deu 25:5. Onan, though he consented to marry the widow, yet, to the great abuse of his own body, of the wife that he had married, and of the memory of his brother that was gone, he refused to raise up seed unto his brother, as he was in duty bound. This was so much the worse because the Messiah was to descend from Judah, and, had he not been guilty of this wickedness, he might have had the honour of being one of his ancestors. Note, Those sins that dishonour the body and defile it are very displeasing to God and evidences of vile affections. (3.) Shelah, the third son, was reserved for the widow (Gen 38:11), yet with a design that he should not marry so young as his brothers had done, lest he die also. Some think that Judah never intended to marry Shelah to Tamar, but unjustly suspected her to have been the death of her two former husbands (whereas it was their own wickedness that slew them), and then sent her to her father's house, with a charge to remain a widow. If so, it was an inexcusable piece of prevarication that he was guilty of. However, Tamar acquiesced for the present, and waited the issue.

Onan knew that the seed should not be his - That is, that the child begotten of his brother's widow should be reckoned as the child of his deceased brother, and his name, though the real father of it, should not appear in the genealogical tables.

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, Gen 38:7.

Judah said unto Onan . . . marry her, and raise up seed to thy brother--The first instance of a custom, which was afterwards incorporated among the laws of Moses, that when a husband died leaving a widow, his brother next of age was to marry her, and the issue, if any, was to be served heir to the deceased (compare Deu 25:5).