THE heart of man is his worst part before it be regenerate, and the best afterwards: it is the seat of principles, and the fountain of actions. The eye of God is, and the eye of the Christian ought to be, principally fixed upon it.

The greatest difficulty in conversion is to win the heart to God; and the greatest difficulty after conversion is to keep the heart with God.

By heart, we are to understand the whole soul, or inner man. Now, look what the heart is to the body, that the soul is to the man; and what health is to the heart, that holiness is to the soul. The state of the whole body depends upon the soundness and vigour of the heart, and the everlasting state of the whole man upon the good or ill condition of the soul.

—John Flavel
Adapted from The Whole Works of the Reverend John Flavel, 5:423.