Came across this comment in Derek Kidner’s commentary on Genesis, while getting ready to preach on Genesis 38:
12ff. Sheep-shearing was a festive time (cf. 1 Sam. 25:4, 11, 36), when sexual temptation would be sharpened by the Canaanite cult, which encouraged ritual fornication as fertility magic. The word for harlot in verses 21, 22 suggests that Tamar posed as a cult-prostitute, perhaps to make doubly sure of her victim. The veil of verse 14 seems to confirm this, since (if Assyrian law is any guide) no prostitute except a (married) cultic one might wear it.
Such was the world into which Judah had married. The prophets (e.g. Hos. 4:14) report its corrupting power over Israel for generations to come.” Kidner, Genesis, 200.
What caught my eye in particular was Kidner’s comment about Judah marrying into the ‘world’ described in the previous paragraph. Do people understand that in marriage we are marrying into a new way of seeing the world, and that way of seeing the world can be beneficial or destructive? You don’t just marry a person, you marry a world that is not your own, and it is one that you will have to live in. Better think carefully about who you marry, then.
A Pilgrim's Theology 