“Behold, the days come, saith the LORD, that the city shall be built to the LORD from the tower of Hananeel unto the gate of the corner. And the measuring line shall yet go forth over against it upon the hill Gareb, and shall compass about to Goath. And the whole valley of the dead bodies, and of the ashes, and all the fields unto the brook of Kidron, unto the corner of the horse gate toward the east, shall be holy unto the LORD; it shall not be plucked up, nor thrown down any more for ever.” Jeremiah 31:38-40 (KJV)
The Lord of all the earth has made a new covenant with Israel. Jeremiah has spoken it in the previous verses. If we apply these verses to the Church of the Lord Jesus Christ alone, then we spiritualize the text, and rob God of the promise He made; and make the promise of no affect to Israel, or the Church.
Of course the city was rebuilt following the return; after 70 total years in Babylon; and the city was destroyed again about 70 A.D. This does not mean that God broke the covenant. This is speaking of a day when all the previous things Jeremiah has spoken in this chapter have come to pass; and that is when Jesus returns in power and great glory and basically rebuilds it Himself.
The people of Israel will see their Messiah Jesus and will believe; and their hearts and minds will be changed by His grace, power and glory. God will not allow one single word He has spoken to fall to the ground void or empty.
Christian this is the evidence we can trust God with our salvation through the cross of Jesus. If He will not keep His covenant with Israel there can be no assurance of our salvation. Look unto Jesus Christ and live forever.