malachi 2:14 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. - Free Bible Online

      14. Wherefore?--Why does God reject our offerings?
      Lord . . . witness between thee and . . . wife--(so Ge 31:49, 50).
      of thy youth--The Jews still marry very young, the husband often being but thirteen years of age, the wife younger (Pr 5:18; Isa 54:6).
      wife of thy covenant--not merely joined to thee by the marriage covenant generally, but by the covenant between God and Israel, the covenant-people, whereby a sin against a wife, a daughter of Israel, is a sin against God [MOORE]. Marriage also is called "the covenant of God" (Pr 2:17), and to it the reference may be (Ge 2:24; Mt 19:6; 1Co 7:10).

JFB.