Verse 11 is the contrast to the previous verses addressed to those who would not believe in Christ. This verse addresses “he that believeth these things which I have spoken.” Those things concern the person and power of the Messiah, the God who condescended to come to earth.
The next question is how one might know that something is true. The answer is a reformulation of “Wherefore by their fruits ye shall know them” (Matthew 7:20 KJV). This formulation is not as succinct, but it connects Good with God.
“Whatsoever thing persuadeth men to do good is of me; for good cometh of none save it be of me.” This good is not only associated with the gospel, but also with all good things humankind may do, even if they may not have the gospel to understand deeper reasons for their actions. There are so many who have lived on earth without the possibility of having known the gospel, and there are many whose good is, and has been, done through a spiritual influence that they perhaps cannot name.
Nevertheless, for those who have the gospel, we understand that our good comes because of the resurrected Christ, who declared “I am the Father, I am the light, and the life, and the truth of the world.”