The Heart
Your heart is the inward you.
It's the will, mind and intellect of who you really are. You are, what you are, based on what's in your heart. It's why the Bible says: for out of the abundance of the heart the mouth speaketh.
Be careful of the words that come out of your mouth, as it's a reflection of what your heart has been meditating upon.
Psalm 19:14 Let the words of my mouth, and the meditation of my heart, be acceptable in thy sight, O LORD, my strength, and my redeemer.
For this reason, outward conduct isn’t always the best estimation of someone.
The Bible also says: The heart is deceitful above all things, and desperately wicked: who can know it?
Because your heart is deceitful, the Bible commands us to diligently keep and guard it.
Proverbs 4:23 Keep thy heart with all diligence; for out of it are the issues of life.