Joshua 1:5-9 The Key to Success

v5 The PROMISE of God’s Presence with us bringing Success in doing His will:
"No man shall be able to stand before you all the days of your life; as I was with Moses, so I will be with you. I will not leave you nor forsake you.”

The COMMAND and PROMISE of success (poetically repeated in v6,7,8,9).
v6: "(1) Be strong (in faith through the Word, believing the promise)
and (2) of good courage, (to act on the Word, possessing the land)
for (3) to this people you shall divide as an inheritance the land which I swore to their fathers to give them (the PROMISE of good success).

v7: "(1) Only be strong (in faith through the Word, believing the promise)
and (2) very courageous (to act on the Word, possessing the land) that you may observe TO DO according to all the law which Moses My servant commanded you; do not turn from it to the right hand or to the left,
that (3) you may prosper wherever you go (the PROMISE of good success).

v8 explains how we can be (1) so we can do (2) so that we can have (3)
"(1) This Book of the Law shall not depart from your mouth,
but you shall meditate in it day and night, that
(2) you may observe to DO according to all that is written in it.
(3) For then you will make your way prosperous,
and then you will have good success. (the PROMISE of success)

v9: "Have I not commanded you?
(1) Be strong (in faith, believing the Word)
(2) and of good courage; do not be afraid, nor be dismayed (to act on Word)
(3) for the LORD your God is with you wherever you go (to give you success in possessing the land).” The PROMISE is put in the same form as in v5.
For more exposition on these verses see: Possessing Our Promised Land