Let it be a settled principle again in our religion, that when a man's general conversation is ungodly—his heart is graceless and unconverted.
Let us not give way to the foolish notion, that no one can know anything of the state of another's heart, and that although men are living wickedly—they have good hearts at the bottom.
Such notions are flatly contradictory to our Lord's teaching. Is the general tone of a man's speech carnal, worldly, godless or profane? Then let us understand, that this is the state of his heart!
When a man's tongue is extensively wrong, it is absurd, no less than unscriptural, to say that his heart is right!
No good tree bears bad fruit; nor does a bad tree bear good fruit. Each tree is recognized by its own fruit. People do not pick figs from thornbushes, or grapes from briers.
The good man brings good things out of the good stored up in his heart; and the evil man brings evil things out of the evil stored up in his heart. For out of the overflow of his heart his mouth speaks!" Luke 6:43-45
J. C. Ryle