Matthew 12:34b-35 - For out of the overflow of the heart the mouth speaks. The good man brings good things out of the good stored up in him, and the evil man brings evil things out of the evil stored up in him.
Jesus tells us to watch what we say. The things we say come from our heart, so if we pay attention to the things that come out of our mouths we can see the condition of our hearts. Before Christ our hearts were evil. We were filled with sin and it was reflected in what we said and did.
Proverbs tells us that “As water reflects a face, so a man’s heart reflects the man.” We see that our hearts are a reflection of who we are. So before Christ we were wicked, our hearts were evil and full of sin and our actions showed this. But Christ came and changed all that.
In Him we are a new creation; we are created like God in true righteousness and holiness. Jesus has taken our old heart of sin and made it new. This does not mean we will not sin, just that we no longer have evil stored up within us.
With Christ in us we now have good in us that should be overflowing from our hearts and out of our mouths. Be careful though! Proverbs also warns us, “Above all else guard your heart, for it is the wellspring of life.” We must protect our heart and what we allow into it. Now that our heart is new we must keep it pure and holy, because when God looks at you He sees your heart.