“Again and again the Christian heart grows weak and begins to falter.Where will we find strength of heart? I don’t mean physical strength. God doesn’t demand physical strength, or health, or even life for that matter. But he does call us to be “strengthened . . . in the inner man (Ephesians 3:16). How does this happen? One answer is very plain: “It is good for the heart to be strengthened by grace, not by foods” (Hebrews 13:9). The heart is strengthened by grace. “Be strong in the grace that is in Christ Jesus” (2 Timothy 2:1). Daily grace is to the heart what daily bread is to the body. It gives strength. Without it we can’t live and we can’t work.”
John Piper, Future Grace (Colorado Springs: Multnomah, 1995), 67-68.