Here "heart" is a metonym for a person's thoughts or mind. Alternate translation: "cause you to understand" (See: [[rc://en/ta/man/jit/figs-metonymy]])
Paul speaks of God's love and Christ's endurance as if they were destinations on a path. Alternate translation: "how much God loves you and how much Christ has endured for you" (See: [[rc://en/ta/man/jit/figs-metaphor]])