Although there is a bit of a contradiction of terms involved because scripture talks about both a heart of stone (bad) and a heart of flesh (good); AND on the other hand that “flesh” in the role of “the mind of the flesh” is “bad”: We can overlook that grammatical peculiarity and understand that what is meant by a heart of flesh in this case is that this heart is “soft” or emotionally responsive, as contrasted with a heart that is “hard” or deprived and devoid of understanding compassion and mercy, and appears as “cold hard logic”.
Pharaoh was to have his “heart hardened” by God, to serve his purpose in refusing to release the Israelites from Egypt.
In putting a heart of flesh back in his people, God was “turning the hearts of the fathers back to the sons” etc. showing this softer aspect of emotion through a reduction of the “hardness” of attitude, sin etc. In other words being confronted with a reality of an action of love, that the resultant true and good response would be an emotional one, providing that the reality of that action of love was sufficiently defined so as to be able to embrace the truth of the wider scenario of the life and death of each and every man.
John says that he comes to live with us, to make his home in us. His Spirit lives in us. Christ lives in us. He lives IN OUR HEART. It is written “for the love of Christ controls me”. The heart, having been cleansed, now becomes that which outworks goodness where previously it outworked evil because it was in captivity to the diabolos within, to sin and its environment. Now it “knows and relies on the love that God has for us”. The heart contains, produces, love, and therefore it is God who is at work in us.
The one who does not love remains in death. God is love. God does because he is. Likewise we must “do” because we “are”. We love because he first loved us.
[the heart is our inner core reality] [Eph 3-17]