Jesus said (earlier in chapter 6) that we were not to judge or condemn people but rather we were to forgive and release them. But He also says, Each tree produces its own fruit. And you can decide and determine what kind of tree it is by the fruit that it bears. We are told not to judge people, but we are told to test the spirit.
The application is in verse 45, The good man out of the good treasure of his heart produces the good. A human being in his natural state cannot produce that good that comes from God’s Spirit. The good of the Lord can only be produced through His Spirit in His people. Once you have the Spirit of God you are able to see clearly the spiritual need of others, and you are able to help them discern, and help show them the way of salvation.