The Holy Spirit does it -- as even the majority of pro-Sunday scholars freely admit.
You are right, it is the Holy Spirit who does it.
Deuteronomy 30:6-7 New King James Version (NKJV)
6 And the Lord your God will circumcise your heart and the heart of your descendants, to love the Lord your God with all your heart and with all your soul, that you may live.
Matthew 22:37-38 New King James Version (NKJV)
37 Jesus said to him, “‘
You shall love the Lord your God with all your heart, with all your soul, and with all your mind.’ 38 This is the first and great commandment. 39 And the second is like it: ‘You shall love your neighbor as yourself.’ 40
On these two commandments hang all the Law and the Prophets.”
2 Corinthians 13:14 New King James Version (NKJV)
14 The
grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Spirit be with you all. Amen.
Ephesians 3New King James Version (NKJV)
14 For this reason I bow my knees to the Father of our Lord Jesus Christ, 15 from whom the whole family in heaven and earth is named, 16 that He would grant you, according to the riches of His glory,
to be strengthened with might through His Spirit in the inner man, 17
that Christ may dwell in your hearts through faith; that you, being rooted and grounded in love, 18 may be able to comprehend with all the saints what
is the width and length and depth and height— 19 to know the love of Christ which passes knowledge; that you may be
filled with all the fullness of God. 20 Now to Him who is able to do exceedingly abundantly above all that we ask or think, according to the power that works in us, 21 to Him
be glory in the church by Christ Jesus to all generations, forever and ever. Amen.
Hebrews 8:7-11New King James Version (NKJV)
Laws of God Written on Our Hearts
7 For if that first
covenant had been faultless, then no place would have been sought for a second. 8 Because finding fault with them, He says: “Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah— 9 not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they did not continue in My covenant, and I disregarded them, says the Lord. 10 For this
is the covenant that I will make with the house of Israel after those days, says the Lord:
I will put My laws in their mind and write them on their hearts; and I will be their God, and they shall be My people.
Romans 7:5-8 New King James Version (NKJV)
The Law of Sin and Death
5 For when we were in the flesh, the sinful passions which were aroused by the law were at work in our members to bear fruit to death. 6 But now we have been delivered from the law, having died to what we were held by, so that we should serve in the newness of the Spirit and not
in the oldness of the letter.
7 What shall we say then?
Is the law sin? Certainly not! On the contrary, I would not have known sin except through the law. For I would not have known covetousness unless the law had said, “You shall not covet.” 8 But sin, taking opportunity by the commandment, produced in me all
manner of evil desire.
Romans 6:1-4 New King James Version (NKJV)
Now We Are Dead to Sin
1 What shall we say then? Shall we continue in sin that grace may abound? 2 Certainly not! How shall we who died to sin live any longer in it? 3 Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? 4 Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life.
Romans 8:1-9 New King James Version (NKJV)
The Law of the Spirit
8
There is therefore now no condemnation to those who are in Christ Jesus, who do not walk according to the flesh, but according to the Spirit. 2 For
the law of the Spirit of life in Christ Jesus has made me free from the law of sin and death. 3 For what the law could not do in that it was weak through the flesh, God
did by sending His own Son in the likeness of sinful flesh, on account of sin: He condemned sin in the flesh, 4 that the
righteous requirement of the law might be fulfilled in us who do not walk according to the flesh but according to the Spirit. 5 For those who live according to the flesh set their minds on the things of the flesh, but those
who live according to the Spirit, the things of the Spirit. 6 For to be carnally minded
is death, but to be spiritually minded
is life and peace. 7 Because the carnal mind
is enmity against God; for it is not subject to the law of God, nor indeed can be. 8 So then, those who are in the flesh cannot please God.
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.
John 20:28-30 New King James Version (NKJV)
28 And Thomas answered and said to Him, “
My Lord and my God!”
29 Jesus said to him, “Thomas, because you have seen Me, you have believed.
Blessed are those who have not seen and yet have believed.”
1 John 3:18-23 New King James Version (NKJV)
Commandments of the New Covenant
18 My little children
, let us not love in word or in tongue, but in deed and in truth. 19 And by this we know that we are of the truth, and
shall assure our hearts before Him. 20 For if our heart condemns us, God is greater than our heart, and knows all things.
21 Beloved, if our heart does not condemn us, we have confidence toward God. 22 And whatever we ask we receive from Him, because we keep His commandments and do those things that are pleasing in His sight. 23
And this is His commandment: that we should believe on the name of His Son Jesus Christ and love one another, as He gave us commandment.
Let’s talk about the laws on your heart. Who put them there? The Spirit, that's who. Those are the laws of the Spirit of life in Christ, to love God with all your heart, mind and strength and your neighbor as yourself. They are NOT the Old Covenant laws of sin and death.
But why do they seem the same? Thou shalt not kill? Love prevents that in your new nature. Thou shalt not steal? Self-control prevents that in your new nature. Thou shalt not commit adultery? Faithfulness prevents that in your new nature. Thou shalt not covet? Peace and contentment prevents that in your new nature. Thou shalt not lie? Kindness prevents that in your new nature. Honor your parents? Longsuffering and gentleness takes care of them for as long as they live. Believing in the name of Jesus Christ? Joy unspeakable!
Whatever you wouldn't want done to yourself, you do to others.
The fruit of the Spirit is love, joy, peace, longsuffering, kindness, goodness, faithfulness, 23 gentleness, and self-control. Against such there is no law. 24 And those
who are Christ’s have crucified the flesh with its passions and desires. 25 If we live in the Spirit, let us also walk in the Spirit. 26 Let us not become conceited, provoking one another, envying one another.
Those who have to STRIVE to be all the above, don't have the law of the Spirit of life in Christ, they are still trying to keep the law of sin and death in THEIR OWN strength. Their carnal nature makes it hard.