Jesus used the word "heart" as the location of the center of the earth in Matthew 12:40. Therefore, it is not a very large leap to view the human heart not only as a centered four-chambered organ, but as the center of our inclinations and/or behaviors. In Matthew 13:15 even the inclinations of a group of people were known to be housed in the heart - "For this people’s heart has become calloused;".
On an individual level, just as James had some heavy words about our tongue (mouth/lips) in James 3:1-12, Jesus has some sobering news about the origin of those words - the heart - in Matthew 15:18-19.
- "But the things that come out of a person’s mouth come from the heart, and these defile them. For out of the heart come evil thoughts—murder, adultery, sexual immorality, theft, false testimony, slander."
Concerning our mind, God encourages us through Paul - Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is—his good, pleasing and perfect will." (Romans 12:2)
Pertaining to his/our words, David asks of the Lord - "Set a guard over my mouth, Lord; keep watch over the door of my lips." (Psalm 141:3)
The way we start loving God with all our heart, mind, soul and strength; the way believers begin showing God's light by our walk in everything we think, do and say is to have the Holy Spirit leading, guiding and directing the whole way. Whatever bubbles up from our heart - screen it through the Holy Spirit. Whatever is conjured up in our mind - screen it through the Holy Spirit. Whatever makes it to our mouth - may it be what the Holy Spirit desires to say. Live A Holy Spirit Screened Life.