The mustard seed is Jeremiah 31:34 which is cited in Hebrews 8:8 and Hebrews 10:16-17, which refer back to Jeremiah 31:33 and 34 This is the covenant he writes on our hearts and our minds, it is the covenant of Love, that 'their sins and lawless acts I will remember no more." That is the mustard seed that grows into loving the Lord with all our heart, and all our mind, and all our strength.
I can afford a bit of speculation on this forum, seeing that much of it does go on throughout the various topics, so I will take the liberty, that is plainly afforded, to indulge here and there in it. I wonder how far off I might be to think that Jesus drew hearts in the sand as he challenged the crowd gathered to stone the adulteress.
Hi Mem, i wrote this last night to explain further;
“Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah… But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts… And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD: for I will forgive their iniquity, and I will remember their sin no more.” (Jeremiah 31:31–34, KJV)
Here, Jeremiah is not speaking about a single moment only. He is speaking about a work of God that has a beginning, a growth, and a completion. The phrase “the days come” shows a future work. The phrase “after those days” shows that it unfolds in stages. This is important. The covenant is promised, but its full condition is very specific: God’s law is written so deeply in the heart that teaching is no longer needed, because “they shall all know Me.” That has never yet happened to the whole people of God.
Jesus Himself began this covenant through His death and resurrection. He said plainly, “This cup is the new testament in my blood” (Luke 22:20). So yes, the New Covenant was truly established by Jesus. But establishment is not the same as full completion. Jesus did not say the Kingdom would appear fully grown in one moment. He said the opposite.
“The kingdom of heaven is like to a grain of mustard seed, which a man took, and sowed in his field: Which indeed is the least of all seeds: but when it is grown, it is the greatest among herbs, and becometh a tree.” (Matthew 13:31–32, KJV)
This parable explains exactly how Jeremiah’s promise unfolds. The Kingdom begins small. It grows. It spreads. It takes time. Jesus did not say the seed instantly becomes a tree. He said it becomes a tree. That means the New Covenant begins with Christ, but it moves toward a future fullness.
When Jesus rose and sent the Holy Spirit, the Spirit did not fall on everyone. It fell on a few, first the apostles, then those who believed. This matches the mustard seed. The Kingdom had begun, but it was still growing. The disciples went out teaching because Jeremiah’s words “they shall teach no more” were not yet fulfilled. Teaching still existed because the covenant had not reached its final measure.
Jesus Himself confirmed that growth and delay are part of the plan. He said, “My kingdom is not of this world” (John 18:36), and He also taught that the end would come only when the message had gone out widely.
“And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.” (Matthew 24:14, KJV)
Jeremiah’s vision points to a time beyond the present age, when the work that began with Christ reaches its fullness at His return. At that time, God’s law will not merely be known outwardly or taught by others. It will be fully written within. Knowing God will no longer be partial, mixed with weakness, confusion, or struggle against sin.
This agrees with what Jesus said about the future state of His people.
“Blessed are the pure in heart: for they shall see God.” (Matthew 5:8, KJV)
Purity of heart is not yet complete in believers now. We are being shaped, corrected, taught, and pruned. But Jeremiah speaks of a day when the heart is fully formed by God Himself. When Christ returns, those who belong to Him will no longer struggle between flesh and spirit. They will know God truly, naturally, and fully, and sin will have no place in them.
So your point stands. The New Covenant has begun, but it has not yet reached its final condition. The mustard seed has been planted. The tree is growing. The disciples were the first branches. The Spirit was the first rain. But the full harvest comes when Jesus returns, when Jeremiah’s words are no longer partially true, but completely true.
At that time, “they shall all know Me” will no longer be hope or promise. It will be reality.
And that is not speculation. That is simply letting Jeremiah explain Jesus, and Jesus explain Jeremiah, in the plain and simple way Scripture itself teaches.
