What is “heart” in this context?

Resolve; energy to continue; courage to face obstacles to wholeness of life.

Thieves: situations; time; others

Keys to Not Losing Heart is Not Losing Focus!

On the ministry of the Holy Spirit in you: 2 Corinthians 3:8, 17, 18

He is our Guide, Teacher, Comforter, Divine Helper [John 14 – John 17]

On His ministry of Righteousness; Our right standing in Him! 2 Corinthians 3:9 [Romans 5:17; 2 Corinthians 5:21]

On the Mercy of God; 2 Corinthians 4:1; Hebrews 4:16

On the Glory of God in the face of Jesus Christ in our inner man: 2 Corinthians 4:6; We take on the likeness of what we continually focus on.

On the ongoing Power of His Cross 2 Corinthians 4:10, 11; 2 Corinthians 4:8, 9; see especially 2 Corinthians 4:5.

Focus away from ourselves and our own lack of ability; own resources, situations, circumstances, feelings

On the Eternal, not the present! 2 Corinthians 4:17, 18