As God's wife, earthly Israel was to maintain spiritually purity in being faithful to Him, which they were not, and which resulted in that God divorced them (Jer 3:8). Further in the chapter, oddly enough, we see that God remarried Israel, but He did so with a different Israel - spiritual Israel. We see this because God declared that He would take "one from a city and two from a family" and that He would be the one to " bring you to Zion" (or Sion). In other words, Israel would no longer be comprised of Jews en-masse as they had been in the first marriage, but instead, taken out of all people which would be brought individually to spiritual Israel (Zion or Sion) as the elect. God could not remarry the first Israel because it would be against His law for Him to do so
[Jer 3:8 KJV]
8 And I saw, when for all the causes whereby backsliding Israel committed adultery I had put her away, and given her a bill of divorce; yet her treacherous sister Judah feared not, but went and played the harlot also.
[Jer 3:14 KJV] 14 Turn, O backsliding children, saith the LORD; for I am married unto you: and I will take you one of a city, and two of a family, and I will bring you to Zion:
[Deu 24:1-4 KJV]
1 When a man hath taken a wife, and married her, and it come to pass that she find no favour in his eyes, because he hath found some uncleanness in her: then let him write her a bill of divorcement, and give [it] in her hand, and send her out of his house.
2 And when she is departed out of his house, she may go and be another man's [wife].
3 And [if] the latter husband hate her, and write her a bill of divorcement, and giveth [it] in her hand, and sendeth her out of his house; or if the latter husband die, which took her [to be] his wife;
4 Her former husband, which sent her away, may not take her again to be his wife, after that she is defiled; for that [is] abomination before the LORD: and thou shalt not cause the land to sin, which the LORD thy God giveth thee [for] an inheritance.
[Heb 12:22 KJV]
22 But ye are come unto mount Sion, and unto the city of the living God, the heavenly Jerusalem, and to an innumerable company of angels,