First off, this is similar to the obedience of faith mentioned in Romans 1:5. Obedience from the heart and the obedience of faith speak to the motivation of obedience….the engine driving obedience….the catalyst or cause of obedience. It is very different in the new covenant than in the old covenant. My assumption is that we believers are really new covenant people.
Again, we need to turn to Hebrews the Rosetta stone of the New Covenant. Heb 8:8-12 ESV For he finds fault with them when he says: "Behold, the days are coming, declares the Lord, when I will establish a new covenant with the house of Israel and with the house of Judah, (9) not like the covenant that I made with their fathers on the day when I took them by the hand to bring them out of the land of Egypt. For they did not continue in my covenant, and so I showed no concern for them, declares the Lord. (10) For this is the covenant that I will make with the house of Israel after those days, declares the Lord: I will put my laws into their minds, and write them on their hearts, and I will be their God, and they shall be my people. (11) And they shall not teach, each one his neighbor and each one his brother, saying, 'Know the Lord,' for they shall all know me, from the least of them to the greatest. (12) For I will be merciful toward their iniquities, and I will remember their sins no more."
Under the new covenant, God’s Law is written on the believer’s hearts and put in their minds. The driver…catalyst…is found in this statement “I will be merciful toward their iniquities and I will remember their sins no more.” The operating force in obedience from the heart is the Sabbath Rest! It is faith in God’s mercy that will ultimately, over time, bring about obedience from the heart….the obedience of faith.
This is precisely why faith and not works is the necessary ingredient. One has to rest in, rely on, cling too and have settled confidence in the fact that God is a God of mercy and that he is not keeping track of sin. In fact, God has forgotten sin under the new covenant. When one really believes this…and it is hard to believe this…. I want to address any who would cry easy believism but, when one really truly trusts God’s veracity in this proclamation it produces supernaturally a deep and abiding and genuine love for God. This deep abiding love for God is the catalyst for obedience….but, it can only work when one is completely resting in Jesus.