You ask, “Why?” It is because the LORD is the witness between you and the wife of your youth. You have been unfaithful to her, though she is your partner, the wife of your marriage covenant.
Has not the one God made you? You belong to him in body and spirit. And what does the one God seek? Godly offspring. So be on your guard, and do not be unfaithful to the wife of your youth.
“The man who hates and divorces his wife,” says the LORD, the God of Israel, “does violence to the one he should protect,” says the LORD Almighty. So be on your guard, and do not be unfaithful.