The heart refers to the central part of a person. The heart is the nature of a person, and to know the heart of someone is to know that person’s innermost character, feelings, or inclinations (see Proverbs 4:23 and 16:1). The heart of God is the essence of who He is, what He desires, His will, and His purposes. By reading the Bible, knowing Jesus, and spending time in prayer, a person can know the heart of God

https://www.gotquestions.org/heart-of-God.html