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.
Yet ye say, Wherefore? - why does God reject our offerings?
Because the Lord hath been witness between thee and the wife - (so Genesis 31:49-50).
Of the youth. The Jews still marry very young, the husband often being but thirteen years of age, the wife younger (Proverbs 5:18; Isaiah 54:6).
Yet is she thy companion, and the 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" (Proverbs 2:17), and to it the reference here may be (cf. Genesis 2:24; Matthew 19:6; 1 Corinthians 7:10).