35 Thus says the Lord - who gives the sun for light by day and the fixed order of the moon and the stars for light by night, who stirs up the sea so that its waves roar - the Lord of hosts is his name: 36 “If this fixed order departs from before me, declares the Lord, then shall the offspring of Israel cease from being a nation before me for ever.” 37 Thus says the Lord: “If the heavens above can be measured, and the foundations of the earth below can be explored, then I will cast off all the offspring of Israel for all that they have done, declares the Lord.”

38-39 “Behold, the days are coming, declares the Lord, when the city shall be rebuilt for the Lord  from the Tower of Hananel to the Corner Gate. And the measuring line shall go out farther, straight to the hill Gareb, and shall then turn to Goah. 40 The whole valley of the dead bodies and the ashes, and all the fields as far as the brook Kidron, to the corner of the Horse Gate towards the east, shall be sacred to the Lord. It shall not be uprooted or overthrown any more for ever.” Jeremiah 31:35-40 (English Standard Version)

In the previous four verses Jeremiah used the phrase 'declares the Lord' four times. In today's six verses he uses that phrase, and the words 'thus says the Lord', another six times. He wanted Israel to know clearly that what he was telling them was what God had made known to him. In verses 31-34 he spoke of the wonderful new covenant God was going to make. The New Testament shows that this covenant was brought about in and through Jesus Christ. What was he now confirming about this covenant, and the one who was making it? (vs 35-37)

He reminded them that their God was not only the one who set the sun, moon and stars in the heavens, but He also appointed those heavenly bodies to keep to the path He had set for them. In the very first chapter of the Bible we read: “God said, 'Let there be lights in the sky to separate day from night. These lights will be used for signs, seasons, days, and years. They will be in the sky to give light to the earth.' And so it happened. God made the two large lights - the brighter light to rule the day, and the smaller light to rule the night. He also made the stars.” Genesis 1:14-16

The point God made through Jeremiah was that Israel’s future was as certain as the continuing existence of the sun, moon and stars. (vs 36) Israel was not going to vanish during the 70 years of exile in Babylon. God is in charge of the roaring nations just as much as He is in charge of the ocean storms. And Verse 37 was grounds for an even deeper hope and confidence on their part. Look at what God said there.

The chances of God forsaking them were as small as the possibility of any of us being able to measure and fully explore the vastness of the heavens and the hidden mysteries of the earth. Even with the amazing advances of science in the last 100 years we can't do that. God's faithful love is way beyond our full understanding. This is why the apostle Paul prayed as he did for Christians in the city of Ephesus. He said: “I pray that Christ will live in your hearts by faith and that your life will be strong in love and be built on love. And I pray that you, and all God’s holy people, will have the power to understand the greatness of Christ’s love - how wide and how long and how high and how deep that love is. Christ’s love is greater than anyone can ever know, but I pray that you will be able to know that love.” (Ephesians 3:17-19 Paraphrase)

In vs 38-39 Jeremiah tells how the ruined city of Jerusalem would be rebuilt and the whole area would be sacred to God again. A physical fulfilment of that took place when the Jews returned in 516BC. But it's greater fulfilment is a spiritual one. Jews and Gentiles who've called on Jesus Christ for salvation are the spiritual Israel who God will never cast off, and who will endure for all eternity. So the writer of the New Testament book Hebrews said of Christians: “You have come to Mount Zion, and to the city of the living God, the heavenly Jerusalem.” (Hebrews 12:22) It is the faithful character and promises of God that gives Christians their confident hope of eternal life.