The promise of the new covenant is one of the most precious of the entire Bible: “‘Behold, days are coming,’ declares the LORD, ‘when I will make a new covenant with the house of Israel and with the house of Judah, not like the covenant which I made with their fathers in the day I took them by the hand to bring them out of the land of Egypt, My covenant which they broke, although I was a husband to them,’ declares the LORD. ‘But this is the covenant which I will make with the house of Israel after those days,’ declares the LORD, ‘I will put My law within them and on their heart I will write it; and I will be their God, and they shall be My people. They will not teach again, each man his neighbor and each man his brother, saying, “Know the LORD,” for they will all know Me, from the least of them to the greatest of them [only those who know Him will be in the covenant],’ declares the LORD, ‘for I will forgive their iniquity, and their sin I will remember no more’” (Jeremiah 31:31-34).
In the new covenant, He writes His Law on the heart of the covenant people (see also Deuteronomy 30:6,8; Proverbs 1:23; Ezekiel 36:26,27)! This promise is fulfilled in Christ (Hebrews 8:6-12; 9:15; 12:24), and proclaimed weekly at the Table of the Lord (Luke 22:20; 1 Corinthians 11:25).
His Law is on the hearts of those who are truly the covenant people. But it doesn’t stay there. Remember this other great promise: “It will come about after this that I will pour out My Spirit on all mankind; and your sons and daughters will prophesy, your old men will dream dreams, your young men will see visions. Even on the male and female servants I will pour out My Spirit in those days” (Joel 2:28,29//Acts 2:16-18). This promise is for all those who “repent” and are “baptized in the name of Jesus Christ for the forgiveness of your sins” (Acts 2:38).
The writing of the Law on the heart is parallel to the pouring out of the Spirit. The Word and Spirit cannot be separated. The presence of the Spirit is manifested by the presence of the Word in the heart. The Law, written on the heart of those in the new covenant by the Lord Himself, does not stay in the heart. The Spirit manifests His Word from the heart of the new covenant community members through “prophesy,” “dreams,” and “visions.” These three manifestations will not deviate in the slightest from the Word of God (or they show themselves to be of a different spirit that is not holy).
In the new covenant, the Lord Himself (through His Word/Law and Holy Spirit) works out obedience to His own command: “These words, which I am commanding you today, shall be on your heart. You shall teach them diligently to your sons and shall talk of them when you sit in your house and when you walk by the way and when you lie down and when you rise up. You shall bind them as a sign on your hand and they shall be as frontals on your forehead. You shall write them on the doorposts of your house and on your gates” (Deuteronomy 6:6-9). I just read this passage to my children last night (we are considering Q.42 of the Westminster Shorter Catechism this week). The Spirit-spoken “prophecy” is none other than the teaching “diligently to your sons” and the “talk...in your house...by the way.” The “dreams” and “visions” are the “talk of them...when you lie down and when you rise up.” This is the blessed man who delights "in the Law of the LORD," and this delight manifests in his "day and night" meditation (Psalm 1:1,2).
Don’t miss the fact that we are to teach our children not just any “words,” but “these words,” commanded by Moses: the Law of God. They will never know their need for Christ apart from “these words” (Galatians 3:22-24). At the same time, don’t miss the fact that you cannot “teach them diligently,” “talk of them,” “bind them,” or “write them” apart from the Holy Spirit, Who speaks His Word/Law from the hearts of those who are the new covenant community in Christ.
“...be filled with the Spirit...fathers, do not provoke your children to anger, but bring them up in the discipline and instruction of the Lord” (Ephesians 5:18; 6:4). The instruction to our children of the Law of God in the power and help of the Holy Spirit in Christ is His great means of grace in our homes.