Give glory to the LORD your God, before he cause darkness, and before your feet stumble upon the dark mountains, and, while ye look for light, he turn it into the shadow of death, and make it gross darkness.
Give glory to the Lord - show by repentance and obedience to God that you revere His majesty. So Joshua exhorted Achan to "give glory to God" (Joshua 7:19) by confessing his crime, thereby showing he revered the all-knowing God.
Before he cause darkness, and before your feet stumble upon the dark mountains - image from travelers stumbling into a fatal abyss when overtaken by nightfall (Isaiah 59:9-10; Amos 8:9).
Dark mountains - literally, mountains of twilight or gloom х haareey (H2022) naashep (H5399)], which cast such a gloomy shadow that the traveler stumbles against an opposing rock before he sees it (John 11:10; John 12:35).
Shadow of death - the densest gloom; death-shade (Psalms 44:19). Light and darkness are images of prosperity and adversity.