Of course repentance is part of the New Testament revelation, the New Testament describes this at length. The fact that you are a sinner has to be revealed to you (Romans 1:18-20), and is. The word of God is described by Jesus as a seed, the soil the seed falls on might be too hard for it to take root, or too shallow for it to mature and bear fruit, it can be crowded out by the cares of this life and deceitfulness of riches described as weeds. Once you receive this seed, that is the basis for conversion, it is impossible if you are
enlightened:
It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, who have tasted the goodness of the word of God and the powers of the coming age. (Hebrews 6:4-5)
To be restored to repentance.
If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame. (Hebrews 6:6)
If you 'fall away'.
This idea of 'enlightenment' is simply the light of New Testament revelation, John puts special emphasis on the light that has come into the world, but men have loved darkness more then light. That enlightenment isn't the same as the ten commandments even though the Law did testify to the righteousness of God. The Law came through Moses as John tells us, but grace and truth came through Christ:
For the law was given through Moses; grace and truth came through Jesus Christ. 18 No one has ever seen God, but the one and only Son, who is himself God and is in closest relationship with the Father, has made him known. (John 1:17-18)
You will not get the gospel of Jesus Christ from the Law or the Prophets, even though all the prophets spoke of him. You can't keep the ten commandments apart from new birth where the heart of stone is replaced by a heart of flesh:
I will also sprinkle clean water on you, and you will be clean. I will cleanse you from all your impurities and all your idols. I will give you a new heart and put a new spirit within you; I will remove your heart of stone and give you a heart of flesh. And I will put My Spirit within you and cause you to walk in My statutes and to carefully observe My ordinances. (Ezekiel 36:25-37)
The Levitical law included far more then the Ten Commandments, there were rites of purification and sacrifice for sin. Only when you receive the Holy Spirit based on faith in the gospel are you remotely capable of observing the will of God expressed in his revealed word. Apparently, the Hebrews after the Exodus were given an opportunity to receive the Spirit on some level but the message was not received by faith.
For we also have had the good news proclaimed to us, just as they did; but the message they heard was of no value to them, because they did not share the faith of those who obeyed. (Hebrews 4:2)
The Spirit swore in his wrath they would never enter into his rest, when they could cease from their labor. Obedience can be had by no other means, you believe the gospel and receive the Holy Spirit. Avoiding the hazards of unbelief and distractions both from carnality and legalism the believer will go on to bear fruit in the fullness of time. You won't get that from the Sinai covenant, most of them were stiff necked and rebellious and in their hearts turned back to Egypt. God almost killed all but Moses but Moses talked God out of it saying don't let it be said you delivered your people out of Egypt only to destroy them in the wilderness.
Your error is evident and obvious, your conflating the commandments of Christ with the Law of Moses,, two very different things. While it is true Christian conversion is marked by repentance and bearing fruit, Christ's commandments are not identical with the Mosaic Law. The Law has to be written on the heart, you must be perfect even as your Father in heaven is perfect, you must be the righteousness of God in Christ which is how your righteousness exceeds that of the scribes and pharisees. The Law made nothing perfect and can make nothing perfect, you must be born again and follow the law of the Spirit. You will not find that at Sinai, the gospel calls us to Zion, the city of the Living God. The dead letter of the Law was nailed to the cross through the power of an indestructible life (Hebrews 7:16). That life is found only 'in Christ', apart from grace and the power of the Holy Spirit you are powerless and lost.
Grace and peace,
Mark