then the husband who divorced her first may not remarry her after she has been defiled, for that is an abomination to the LORD. You must not bring sin upon the land that the LORD your God is giving you as an inheritance.
The first husband may not marry her again after her second marriage, because that would be an abomination and would bring sin upon the land God gives Israel.
This verse gives the central prohibition and grounds it in the holiness of the land.
1If a man marries a woman, but she becomes displeasing to him because he finds some indecency in her, he may write her a certificate of divorce, hand it to her, and send her away from his house. 2If, after leaving his house, she goes and becomes another man’s wife, 3and the second man hates her, writes her a certificate of divorce, hands it to her, and sends her away from his house, or if he dies, 4then the husband who divorced her first may not remarry her after she has been defiled, for that is an abomination to the LORD. You must not bring sin upon the land that the LORD your God is giving you as an inheritance. 5If a man is newly married, he must not be sent to war or be pressed into any duty. For one year he is free to stay at home and bring joy to the wife he has married.