“Study this Book of Instruction continually. Meditate on it day and night so you will be sure to obey everything written in it. Only then will you prosper and succeed in all you do (Joshua 1:8 NLT).”
From Gill Commentary:
“This book of the law shall not depart out of thy mouth.”
He was often to read it, frequently repeat it, and speak of it, to refresh his own memory with it, and the memory of those about him. . .
“But thou shalt meditate therein day and night.”
Whenever he had any leisure from the important business of his office, whether by day or night, see Psalm 1:2 (below).
“But they delight in the law of the Lord , meditating on it day and night.”