Matthew 15:18-19

But whatever (Word) comes out of the mouth comes from the heart, and this is what defiles and dishonors the man. For out of the heart come evil thoughts and plans, murders, adulteries, sexual immoralities, thefts false testimonies, slanders.  

What we have inside our hearts and thoughts in our minds is what we will speak. We will talk about those things if we are angry, troubled, or dissatisfied. Now, if God is at the center of our hearts, we will talk about what is pure and lovely. We can gauge where we are with God and our walk by what is spoken out of our mouths.