Some point to Genesis 24 and the story of Isaac and Rebekah as an example of a couple being married solely by sexual intercourse, without any type of ceremony. But the details that lead up the marriage reveal that a formal process was followed. Isaac’s father, Abraham, gave his servant a list of things to do to find Isaac a wife (Genesis 24:1–10)
We know that God does not equate sexual intercourse with marriage based on the fact that the Old Testament often distinguishes a wife from a concubine. Also, 1 Corinthians 7:2 indicates that sex before marriage is immorality.
According to Catholic Answers – the largest lay-run apostolate of Roman Catholic apologetics and evangelization in the United States, It is, historically certain that from the beginning of the thirteenth century the sacramental character of marriage was universally known and recognized as a dogma.
Ye should therefore know that “Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge.” Hebrews 13:4.
“But I say to the unmarried and the widows: It is good for them if they remain even as I am; but if they cannot exercise self-control, let them marry. For it is better to marry than to burn with passion.” 1 Corinthians 7:8-9.
Credits: Catholic Answers, Gee Bees “A love so right”, Get Question Ministry