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.
NIV
Yet you ask, Why does He reject it? Because the Lord was witness [to the covenant made at your marriage] between you and the wife of your youth, against whom you have dealt treacherously and to whom you were faithless. Yet she is your companion and the wife of your covenant [made by your marriage vows].
AMP
Yet ye say, Wherefore? Because the LORD hath been witness between thee and the wife of thy youth, against whom thou hast dealt treacherously: yet is she thy companion, and the wife of thy covenant.
KJV
So when the time came for Merab, Saul's daughter, to be given to David, she was given in marriage to Adriel of Meholah.
NIV
But at the time when Merab, Saul's daughter, should have been given to David, she was given to Adriel the Meholathite as wife.
AMP
But it came to pass at the time when Merab Saul's daughter should have been given to David, that she was given unto Adriel the Meholathite to wife.
KJV
Therefore, do not give your daughters in marriage to their sons or take their daughters for your sons. Do not seek a treaty of friendship with them at any time, that you may be strong and eat the good things of the land and leave it to your children as an everlasting inheritance.'
NIV
Therefore, do not give your daughters to their sons or take their daughters for your sons; and never seek their peace or prosperity, that you may be strong and eat the good of the land and leave it as an inheritance to your children always.
AMP
Now therefore give not your daughters unto their sons, neither take their daughters unto your sons, nor seek their peace or their wealth for ever: that ye may be strong, and eat the good of the land, and leave it for an inheritance to your children for ever.
KJV
But when John rebuked Herod the tetrarch because of his marriage to Herodias, his brother's wife, and all the other evil things he had done
NIV
But Herod the tetrarch, who had been [repeatedly] told about his fault and reproved with rebuke producing conviction by [John] for [having] Herodias, his brother's wife, and for all the wicked things that Herod had done
AMP
But Herod the tetrarch, being reproved by him for Herodias his brother Philip's wife, and for all the evils which Herod had done,
KJV