wash your feet: David assumed that Uriah would have sex with Bathsheba while on this weekend pass. Then everyone except Bathsheba would assume that the child was Uriah’s, conceived on this night.
a gift: David may not have cared whether Uriah and Bathsheba were actually intimate. If Uriah had gone back to his house, people would have assumed that the pregnancy began during that time. This would have prevented questions about when and how Bathsheba became pregnant.