I have heard it proposed that marriage is a sacrament by virtue of its being efficacious by divine right. Undoubtedly we know it to have been instituted by God, as affirmed by Christ with the authority of the Old Testament:
And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female, and said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh? Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.
Malachi seems to bear this out: 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. The prophet continues, as rendered by the ESV (the Authorized Version differs), Did he not make them one, with a portion of the Spirit in their union?
It may seem, then, that holy Scripture teaches more than two sacraments, perhaps even seven. Of ‘those five commonly called Sacraments, that is to say, Confirmation, Penance, Orders, Matrimony, and Extreme Unction’, the Thirty-Nine Articles cite this difference: they ‘have not like nature of Sacraments with Baptism, and the Lord’s Supper, for that they have not any visible sign or ceremony ordained of God.’ This lack notwithstanding, the Scriptures do teach that marriage actually accomplishes something in the sight of God, indeed (one may say) by the agency of God.
Like holy orders, but also like coronation, marriage is a politically efficacious covenant that (if valid) God ratifies, and for which he gives grace, especially if it’s contracted between Christians. By the sanction of God, something real happens. The king becomes head of a nation, the husband head of a household; with God’s help they rule out of the love that their offices require.
But the sacraments, properly called, are spiritually efficacious with faith, the others only temporally so. At death, bishop is no longer bishop, king is no longer king, husband is no longer husband, for death has dissolved those bonds of earth that distinguish even male and female; for in Christ, says the Apostle – that is, spiritually – there is no male nor female. But the spiritual sacraments (or gospel sacraments), despite likewise being ministered at the hands of men, having also effectually signified union with Christ, with promise attached to that effect, have prevailed beyond death: therefore these are the two, baptism and the supper of the Lord, that we properly call sacraments.