"And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh." Ezekiel 36:26, ESV)
The people of Israel became unruly, idolatrous, and hardened against God. Even after breaking the conditions of their first covenant with Him, nevertheless, He promised to make a new covenant with them. This time He promised to give them a new heart of flesh, instead of a heart of stone, and a spirit of grace through the power of the Holy Spirit.
Man's nature was infected with selfishness and evil desires. The entire population was filled with pride and boastfulness as we saw in the very beginning with Adam and Eve. All humanity had a tendency towards disobedience and unfaithfulness. But God in His grace, promised to give them a new heart. He promised to purify their heart and cleanse their inner soul, through the shed blood of a sinless Mediator. “I will give you a new heart, and a new spirit I will put within you,” was God's promise to His people, “and I will remove the heart of stone from your flesh, and give you a heart of flesh.” God was to remove the rock-hard, heart of stone and replace it with a heart that is obedient to the Lord and responsive to His word.
This amazing promise to mankind was to be fulfilled in the person and work of Jesus Christ and would come through the power of God's own Holy Spirit. The cold, hard, and unyielding heart of the unregenerate man, with its self-centered desires was to be renewed and replaced with a soft, clean heart of flesh, in which the Holy Spirit of God Himself was to dwell. The eternal God of the universe was to dwell in the heart of the man who lives by faith and to reign there as King in sovereign power. The human heart, which had become so infected with sin, was to be changed and cleansed, so as to become a holy dwelling place for the God of gods and King of kings. This wonderful promise was finished at Calvary and is fulfilled in the life of all who trust in the Lord Jesus Christ, as the Saviour of their soul and the Mediator for their sins.