God is calling His people to repent.
Fallow ground is uncultivated farmland. Land that was ploughed before but now has been dormant for an extended period. Land that was fruitful at one time has become hardened over time. And unless it is ploughed and broken up, no useful crop can be grown on it.
Fallow ground implies resistance. To break up fallow ground is hard work. The Lord says, do not sow among the thorns. It is not that fallow ground does not yield anything, it only yields weeds and thorns. Nothing useful comes out of it. Fallow ground needs work and preparation to be made useful.
Jeremiah is using circumcision as a metaphor. Spiritually speaking, Judah was to work on having repentant, prepared hearts. They were to return to the Lord with hearts softened by repentance. God is interested in the inward change of heart rather than the physical conformity to rules. Ultimately, it is not the physical circumstance but a changed and purified heart that the Lord desires.
A circumcised heart is a pure heart separated unto God (Romans 2:29), a heart that is aware of its own sin and the need for God’s forgiveness. True circumcision is a matter of the heart, performed by the Spirit of God. Only the Holy Spirit can purify a heart and set us apart unto God. And only when our hearts are ploughed and prepared by the Spirit, can we be used by the Lord.
Is yours a circumcised heart?
Spirit God, purify my heart, I pray.