דברי הימים א כא:כ פירוש: רש״י

hid from the angel, to fulfill the verse (Isa. 26:20): “Go, My people, come into your chambers and close your door about you; hide for but a moment, until the wrath passes.” And Scripture also says (Exod. 12:22): “... as for you, none of you shall go out of his house until morning.”

and Ornan was threshing wheat since Scripture states further (verse 23): “and the wheat for a meal offering,” lest you wonder how wheat was there.