Which Judaism did David Practice?

Reading 1 Samuel in which two oddities have struck me.

The first is: Why is there an idol handy for David's wife - and Saul's daughter - to stuff under the blankets while David escapes? (1 Samuel 19:13)

The second, related issue is: Why does 1 Samuel keep mentioning sacrifices taking place in Bethlehem? Were sacrifices not limited to the the temple in that period?

Idols. Family Sacrifices. Asherah Figurines. It is hard for me to imagine how anyone can read the Old Testament and conclude that Judaism is this monolithic, eternally unchanging institution. In fact, this is becoming one of my litmus tests for evaluating the claims of scholars (and pseudo-scholars).