“The Lord says:
"These people come near to me with their mouth
and honor me with their lips,
but their hearts are far from me.
Their worship of me
is made up only of rules taught by men.” Isaiah 29:13
Jesus quotes this in Matthew 15:8, 9
There are God given escape valves in people that keep people from exploding. They are instantaneous reactions. They include laughter and tears. Another is the mouth. “Out of the overflow of the heart the mouth speaks.” The cure of a bad mouth is to keep good stored up in the heart.
However, not everything that comes out of the mouth comes from the heart. Some of it comes from the heart. Some of it comes from things they have been taught by men whether true or false. In Isaiah 29:13, it is rules taught by men.
This is why people can recite sound doctrine and soon after lose their temper at home. The second event was the overflow of the heart.
The real person is the heart person, not the head person. We should not deceive ourselves or be deceived by others. That does not say we or they are lying. It says that we are two persons, the one taught by men and the person of the heart. Can they be the same? Yes, but it is not automatic.
We can teach children that it is wrong to lie. That is not the same as teaching children not to lie. The second is teaching the heart. The first is teaching the head.
Everything out of the mouth does not come from the heart.