Why Did Rachel Steal the Terafim?

When departing the house of Lavan, the chumash records two types of theft - Rachel stealing the terafim and Yaakov stealing "Lavan's heart" (גניבת דעת/deception).

What are terafim? Are they idols (Lavan calls them his gods but when Rachel takes them they're called terafim)? Why did she steal them? If Rachel was going to steal them, why not just destroy them if they're idols! What did she do with them?

What does "terafim" mean in Shmuel Aleph when Michal uses them to make it look as if David was in bed?

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Delivered at the OU Israel Center, January 16th, 2019 (10 Shevat 5779)