Passage
This book of the law shall not depart out of thy mouth, but thou shalt meditate thereon day and night, that thou mayest observe to do according to all that is written therein: for then thou shalt make thy way prosperous, and then thou shalt have good success.
Nearby Context
Joshua 1:6 Be strong and of good courage; for thou shalt cause this people to inherit the land which I sware unto their fathers to give them.
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 1:8 This book of the law shall not depart out of thy mouth, but thou shalt meditate thereon day and night, that thou mayest observe to do according to all that is written therein: for then thou shalt make thy way prosperous, and then thou shalt have good success.
Joshua 1:9 Have not I commanded thee? Be strong and of good courage; be not affrighted, neither be thou dismayed: for Jehovah thy God is with thee whithersoever thou goest.
Joshua 1:10 Then Joshua commanded the officers of the people, saying,
Study Lenses
The verse centers on "book", "shall", "depart", "mouth", "thou", "shalt", "meditate", and "thereon". It is saying that the verse draws attention to "book" and "shall", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 7's "Only be strong and very courageous to..." into verse 9's "Have not I commanded thee Be strong...", so "book" and "shall" belong inside that flow. In Joshua context, the local focus is covenant, worship, and faithfulness.
A plain takeaway is to answer the verse's own emphasis on "book" and "shall" with trust shaped by these words, not by a vague optimism outside the passage.