Beloved, I pray that you may prosper in all things and be in health, just as your soul prospers. (III John 1:2 NKJV)
Here the Apostle is praying that they would prosper in all things and be in good health. God wants us to prosper in all things and be in good health. There are at least two reasons why God would want us to prosper.
The first reason God wants us to prosper is so we can bless others. We can minister or serve others. Meet the needs of the people around us. We are to do the work that He has called us to do.
The second reason God wants us to prosper is so He can receive the glory. People will notice when we prosper that it is not about us but about Him. They will know beyond a shadow of a doubt that God made us prosper. They will see how we handle every situation. They will see how we prosper over every obstacle.
This will happen as we focus on Godly things so our soul can prosper. If we seek first His Kingdom and His righteousness then our soul will prosper (Matthew 6:33). When our soul prospers then we will prosper in all things and be in good health.