'Heart' in the Bible

Everyone who hates (works against) his brother [in Christ] is [at heart] a murderer [by God’s standards]; and you know that no murderer has eternal life abiding in him.

But whoever has the world’s goods (adequate resources), and sees his brother in need, but has no compassion for him, how does the love of God live in him?

Little children (believers, dear ones), guard yourselves from idols—[false teachings, moral compromises, and anything that would take God’s place in your heart].