"Beloved, I wish above all things that thou mayest prosper and be in health, even as thy soul prospereth." (3 John 2)
In Christ, we are accepted in the Beloved (Ephesians 1: 6)
Paul's first prayer in Romans is that he would have a prosperous journey (Romans 1: 10)
And one of the last prayers recorded for us in the Bible, in the Third Epistle of John, regards our prosperity, which is material, since the author also references soul prosperity in the end.
The key to all prosperity in Christ is that we walk in the truth (3 John 3-4)
What is the truth which John is writing about?
The truth of the Gospel:
"And ye shall know the truth, and the truth shall make you free." (John 8: 32)
This truth is not just the Word of God, for the Jewish leaders whom Jesus was talking to knew the law.
John defines truth, which is defined with grace:
"For the law was given by Moses, but grace and truth came by Jesus Christ." (John 1: 17)
Grace and truth are recognized as one entity in the original Greek, and Paul speaks at length of the Gospel of grace (Galatians 2: 4, 14)
Our soul is prospering as we continue to believe and rest in the Finished work of Jesus, that in Him all our sins are put away, and that as we grow in grace and knowledge of the Lord, we find that the attacks of the enemy have no longer any hold over us!
You do not have to make your soul prosper. Believe on Him whom the Father has sent for you (John 6: 29), and let Him prosper you (Genesis 39: 2)