What does Malachi 2:15 mean?

Didn't God make you one? In body and spirit, you belong together. And what does God want from that union? Children who are faithful to Him. So guard your heart, and don't betray the wife you married when you were young. Malachi 2:15 - Modern Text Bible

(God values faithfulness in marriage, both for the relationship itself and for raising children who know Him.)