They abandoned their idols there, so David and his men carried them away.
— Second Samuel 5:21
David and his men also carried away the idols the Philistines left behind while fleeing from his army. Perhaps David’s soldiers thought of them as souvenirs or trophies and put them in their own homes. Besides failing by having many wives and concubines, David failed by not taking a strong stand regarding idols.
This seems to have been an old problem with David. Much earlier, when David was running from Saul, his wife had used a household image to trick those who sought to kill him (1 Sam. 19:13).
Adapted from David: After God’s Heart, page 93.