What I do without thinking says more about me than what I do when I have plenty of time to process my response. If I don't like my gut response, it's the clearest indicator for me that something is wrong inside. If I respond on a whim in a way that reflects the character of God, it's the clearest indicator that God is in me.
Jesus was right. Out of the overflow of the mouth the heart speaks.
Good people bring good things out of the good stored up in their heart, and evil people bring evil things out of the evil stored up in their heart. For out of the overflow of the heart the mouth speaks. -Luke 6:45Perhaps this is why Solomon warned as well.
"Above all else, guard your heart, for everything you do flows from it." - Proverbs 4:23