Jeremiah 31 34: When God says He will remember their sins no more, He does not mean He will forget Israel's sins, for this would make God not omnicient. God simply means he will not bring their sins to mind.
Jeremiah 31 35 and 36: ""thus saith the Lord which giveth the sun for a light by day the ordinances of the moon and of the stars for a light by night which divideth the sea when the waves thereof roar the Lord Of Hosts His name if those ordinances depart from before me saith the Lord the seed of Israel also shall cease from being a nation before me for ever"
As long as the sun shines by day and the moon and stars shine by night, God's people Israel will remain on Earth. This passage is talking about his physical people Israel, who today are the Anglo-Saxon, Germanic, Scandinavian, Celtic and kindred people.
Jeremiah 33 provides a picture of what the ancient land of Israel would be like after the Babylonian exile was over. It also provides a paralel picture of what the millenial reign will be like. Praise God!