Contextual Biblical Reading Journal:Proverbs 10:11

"The mouth of the righteous is a fountain of life, but violence overwhelms the mouth of the wicked."

This is the wisdom of God about true wisdom to know the differences between a Godly character and an ungodly character, you can tell if someone is a Christian (being of God) to be a child of God or not because we are made His child by adoption upon salvation because we were separated from God through the first sin of mankind by Adam and Eve. 

Jesus's standard guideline about showing fruit is specific proof to show if God is in you by His Holy Spirit or if the devil is in you by the anti-Christ spirit that comes into play.

Everyone is in the image of God, BUT this is observing another's heart to see if they're for or against God based on that fruit of what comes out of their mouth by how they speak and how they act by how they carry that out in themselves as to if they really love God by their lifestyle, and this is a judgment action we are to perform unhypocritically when examining others not to judge over the unimportant things but to point out to help others not bearing the image of Christ truly if they're unsaved whether believing in something else, someone else, or nothing accept God Jesus and just professing lukewarm Christians in facade. 

You have to fear the Lord in honoring respect for the character of the Christian of Christ to be displayed in you because of your love for God, and in that, God only woos you in choosing to love Him freely. 
The righteous are saints who've got a new heart from God, we've still got a wicked deceiving heart but God gives us a new one from Him that's His to act in to demonstrate His Godly characteristics to properly bear His image for us being made in His likeness that we are to identify in when we're saved.

The righteous will speak and act with integrity, sharing, truthfulness, wisdom, wholesomeness, and loving talk whereas the wicked will speak and act with degrading, filthy, ignorant, greedy, selfish, and hateful talk.
This helps to protect you from those who claim Christ only to deceive you because God knows the truth of their heart if they honor or reject the Lord in ignorance that they refuse to acknowledge because even though they say their words, their heart literally tells on them.