Pre-nups are for folks with big money, and big money they would miss losing in a divorce; so they have never been an issue in my family

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Pre-nups are not sinful in themselves, they are just contracts, and may even be useful in the right circumstances. If your daughter is planning on marrying an obvious jerk (obvious to you, not to her), say a guy who has a history of misleading females for his own benefit, you might find yourself wanting her to arrange a pre-nup. It sends a message to both parties to stick to the traight and narrow during marriage and removes all incentive for one partner to stray or to initiate a divorce at all.
Sadly, half of all Christian marriages end in divorce, with or without pre-nups.