Eze 36:26-27 I will give you a new heart and put a new spirit within you; I will take the heart of stone out of your flesh and give you a heart of flesh. I will put My Spirit within you and cause you to walk in My statutes, and you will keep My judgments and do them.
God demonstrated this new heart of flesh in the life of our Lord Jesus Christ.
Wickedness of Men's Heart
Gen 6:5 Then the LORD saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually.
Since the fall of Adam, men has been getting more and more wicked, that even our Jesus did not trust men. Yet out of His great love for us, He died for us, who are unworthy of His trust.
John 2:24 But Jesus did not commit Himself to them, because He knew all men, and had no need that anyone should testify of man, for He knew what was in man.
Stiff-necked and Rebellious Jews
Deu 9:6-7 "Therefore understand that the LORD your God is not giving you this good land to possess because of your righteousness, for you are a stiff-necked people. Remember! Do not forget how you provoked the LORD your God to wrath in the wilderness. From the day that you departed from the land of Egypt until you came to this place, you have been rebellious against the LORD."
Even His anointed Jewish Priesthood and servants with the Holy Spirit were not able to keep Moses' Law, thus needing a new heart of love.
Mat 23:2-3 saying: "The scribes and the Pharisees sit in Moses' seat. Therefore whatever they tell you to observe, that observe and do, but do not do according to their works; for they say, and do not do."
Grace through our Lord Jesus
John 1:14 And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth.
The Word was made flesh in the Person of our Lord Jesus Christ. He was full of:-
Grace - love, compassion, mercy, forgiveness, kindness, generosity, etc.
Truth - wisdom, understanding, knowledge of God, and set free from worldliness, lusts, lies, wickedness.
Spirit of Christ
Rom 8:9 But you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His.
Brethren, With the Spirit of Christ dwelling in us, we will have His grace and truth (new heart filled with His love) so that we will be kind, gracious, helpful, merciful to our brethren and to forgive, protect, support, provide, encourage and most of all to love one another as our Lord Jesus Christ had loved us.
1John 3:16-17 By this we know love, because He laid down His life for us. And we also ought to lay down our lives for the brethren. But whoever has this world's goods, and sees his brother in need, and shuts up his heart from him, how does the love of God abide in him? My little children, let us not love in word or in tongue, but in deed and in truth. And by this we know that we are of the truth, and shall assure our hearts before Him.
1John 2:4 He who says, "I know Him," and does not keep His commandments, is a liar, and the truth is not in him. But whoever keeps His word, truly the love of God is perfected in him. By this we know that we are in Him.
Many Christians, pastors and church leaders claim that they know and love God, and even memorize and constantly teach His attributes, promises and miracles, but God called them liars, because they did not keep His commandments nor words.