"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."

On Keeping the Heart is a discourse upon Proverbs 4:23, "Keep thy heart with all diligence; for out of it are the issues of life." Flavel intended this treatise for the specific purpose of illuminating, healing, and guarding the heart. He had the strong conviction, that saints should be marked by their holiness, therefore matters of the heart were of the utmost importance in the Christian life.