Marriage.
Archimandrite Nikifor’s Biblical Encyclopedia
The institution of marriage dates to the original creation of man. Seeing that it was not good for man to be alone, God made him a help meet for him (Gen. 2:18). According to the teaching of the Orthodox Church, marriage is a sacrament in which, upon the free promise before the priest and the Church of mutual conjugal fidelity by the bridegroom and bride, the marital union of them is blessed as an image of the spiritual union of Christ with the Church, and grace is entreated for them for pure unanimity, for a blessed bearing of children, and their Christian upbringing.
That marriage is a sacrament is evident from the epistle of the Holy Apostle Paul to the Ephesians (5:31, 32). For more on marriage, see Verkhovsky’s “Biblical Dictionary,” pp. 230–236, and the dictionary of Archpriest Solyarsky, vol. 4, pp. 709–711.