Give glory, etc. - Show by repentance and obedience to God, that you revere His majesty. So Joshua exhorted Achan to “give glory to God” by confessing his crime, thereby showing he revered the All-knowing God.
stumble - image from travelers stumbling into a fatal abyss when overtaken by nightfall (Isa 5:30; Isa 59:9, Isa 59:10; Amo 8:9).
dark mountains - literally, “mountains of twilight” or “gloom,” which cast such a gloomy shadow that the traveler stumbles against an opposing rock before he sees it (Joh 11:10; Joh 12:35).
shadow of death - the densest gloom; death shade (Psa 44:19). Light and darkness are images of prosperity and adversity.