Proverbs 4:23 Above all else, guard your heart, for everything you do flows from it.
Romans 12:2 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.
Colossians 3:1-2 Since, then, you have been raised with Christ, set your hearts on things above, where Christ is, seated at the right hand of God. Set your minds on things above, not on earthly things.
Philippians 4:7 And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus.
Taking thoughts captive
Guarding our hearts also includes taking ungodly thoughts captive before they have a chance to lodge themselves into our hearts and ultimately our actions (2 Corinthians 10:3–5).