Albert Barnes Commentary Joshua 1:7

"Only be strong and very courageous, to observe to do according to all the law, which Moses my servant commanded thee: turn not from it to the right hand or to the left, that thou mayest have good success whithersoever thou goest." — Joshua 1:7 (ASV)

Prosper - See the margin. The literal rendering should be retained here since the notion of prosperity is separately introduced by a different word in (Joshua 1:8).