In this verse, God speaks to Joshua and reminds him to keep the book of the law always on his mind, to meditate on it day and night, so that he may be careful to do everything written in it. God promises to be with Joshua and to give him success wherever he goes. This verse encourages us to make God's word a central part of our lives, to reflect on it constantly, and to trust in His presence and guidance.
The Bible is divinely inspired, and Joshua stands as a model of a faithful servant who embraced and applied the teachings of God. He comprehended the significance of listening to God's Word and reflecting upon it. Joshua understood that disregarding the Lord's commands would lead to consequences, and, much like Mary of Bethany, he recognized the importance of heeding the Lord's voice and constantly contemplating His teachings. 
Like Joshua, it is wise for us to heed God's Word, to recite it in our mind, to keep its truth always on our lips and in our hearts, and to follow all that is written in it. Doing so will bring us success and prosperity in all we do, for our benefit and for God's glory.

Dear Heavenly Father, I pray that I may follow the example of Joshua, who listened to Your Word and acted upon it. Help me to recite Your Word constantly in my mind and keep it always on my lips and in my heart. Grant me the wisdom to understand Your Word and the courage to obey it. May I prosper and succeed in all that I do, to Your glory and my benefit. I trust in Your promises and Your guidance, always.
In Jesus's name I pray. Amen.