John Calvin Commentary Genesis 38:2

"And Judah saw there a daughter of a certain Canaanite whose name was Shua. And he took her, and went in unto her." — Genesis 38:2 (ASV)

And Judah saw there a daughter of a certain Canaanite. I am not satisfied with the interpretation that some give of “merchant” for the word Canaanite. For Moses charges Judah with perverse lust, because he took a wife from that nation with which the children of Abraham were divinely commanded to be in perpetual strife.

For neither he nor his other brothers were ignorant that they sojourned in the land of Canaan under the stipulation that afterwards their enemies were to be cut off and destroyed, so that they might possess the promised dominion over it. Moses, therefore, justly regards it as a fault that Judah should entangle himself in a forbidden alliance; and the Lord, eventually, cursed the offspring thus resulting for Judah, so that the prince and head of the tribe of Judah might not be born, nor Christ himself descend, from this union.

This also should be counted among the trials of Jacob’s patience: that a wicked grandson was born to him through Judah, whose sin Jacob was not ignorant of. Moses says that the youth was cut off by the vengeance of God. The same thing is not said of others whom a sudden death has swept away in the flower of their age.

I do not doubt, therefore, that the wickedness for which death was the immediate punishment was extraordinary and known to all people. And although this trial was in itself severe for the holy patriarch, yet nothing tormented his mind more than the thought that he could scarcely hope for God’s promise to be so confirmed that the inheritance of grace would remain in the possession of wicked and abandoned men.

It is true that a large family of children is regarded as a source of human happiness. But this was the particular circumstance of the holy patriarch: though God had promised him a chosen and blessed seed, he now saw an accursed progeny increase and spring up alongside his offspring, which might destroy the expected grace.

It is said, that Er was wicked in the sight of the Lord, (Genesis 38:7). Nevertheless, his iniquity was not hidden from people. Moses, however, means that he was not merely infected with common vices, but rather was so addicted to crimes, that he was intolerable in the sight of God.