Marriage is not just an agreement recognised only by the laws of society but it also has an eternal value through the Mystery of Marriage – and becomes an eternal union in Christ.
Tertullian (2nd century) writes about marriage saying that it is “ordained by Church and confirmed by sacrifice [Eucharist] sealed by blessing and written in Heaven by angels”. Any Christian couple who wanted to get married had to pass through civil formalities that made it valid in the secular society and then, by taking part at the Sunday Mass, in the presence of the entire local Christian community, they received the blessing of the priest.
Their civil agreement became also a “mystery” with eternal value, that transcends their earthly lives, because it was also “written in Heaven”, and not only in a secular register. It became an eternal union in Christ.
(Translation from John Meyendorff, Căsătoria ‒ perspectiva ortodoxă, Editura Renașterea & Editura Patmos, Cluj-Napoca, 2012, p. 35)