In this verse, God promises to be with Joshua as he leads the Israelites into the Promised Land. He reminds Joshua that he must be strong and courageous, and that he must meditate on the law day and night, in order to be successful. He assures Joshua that wherever he goes, He will be with him and that he will not fail. This verse encourages us to trust in God's presence and guidance, and to meditate on His word, as we navigate life's challenges. 
In the same vein as God's people who were slaves to Pharaoh and slaves in Egypt, this precious promise applies to God's people today who were freed from slavery and subjection to Satan. It is all a matter of faith in God's promises - of trusting His Word - of believing the truth of His Scripture. Remember, when you trust in the Lord and follow His commands, He will be with you and you will not fail.
While Israel fought physical battles when it entered the Promised Land, using spears, swords, and shields, the weapons that we use to fight are not those of the world. Instead, they are spiritual weapons that will defeat all our spiritual enemies, and they are all found in Christ.

Dear Heavenly Father, I pray for Your guidance and strength as I navigate life's challenges. Just as You promised to be with Joshua, I trust that You are with me and will be with me everywhere I go. Help me to be strong and courageous in the face of adversity. I will meditate on Your law day and night, so that I may be successful in all that I do. I know that wherever I go, You will be with me, and I will not fail. Thank You for Your constant presence and love.
In Jesus's name I pray. Amen.