In Deuteronomy 22:13-30 and 24:1-4 we have judgments on matters related to marriage.
This case was to be brought by the wife's parents to the elders of the city. If the husband's charge was proved to be unfounded, the elders were to take the man, chastise him, fine him one hundred shekels of silver, and give it to the wife's father. She was to remain the man's wife; he could not send her away all his days (vv. 13-19). But if the husband's claim was true, and the wife was not found to be a virgin, they were to bring her out to the entrance of her father's house, and the men of the city were to stone her to death (vv. 20-21).
In verse 22 we have the case of a man lying with a woman married to a husband. In this case both were to be put to death. Thus the evil of fornication was to be utterly removed from Israel. God is merciful and compassionate, but He does not want His people to be defiled in His sight. Therefore, in a case such as that in verse 22, the sentence was to be immediate and thorough.
In verses 23 and 24 we have the case of a man lying with an engaged virgin in the city. Both of them were to be stoned to death at the gate of the city, because the girl did not cry out in the city and because the man humbled his neighbor's wife.
The expression his neighbor's wife in verse 24 indicates that, in the sight of God, engagement is equal to marriage. This means that, in God's view, once a man and woman have become engaged, they are husband and wife. Thus, canceling an engagement is equal to divorce. This is illustrated by the case of Mary and Joseph in Matthew 1. Mary had been betrothed, engaged, to Joseph, but because she was with child, he was considering to "put her away." However, the angel said to Joseph, "Fear not to take Mary your wife" (Matt. 1:20). This indicates clearly that, although they did not come together until after the birth of Jesus (v. 25), they were nevertheless married in the sight of God.
Since in the eyes of God engagement is equal to marriage, I would urge the young people to take the matter of engagement very seriously. Marriage should be approached with fear and reverence. For a sister to be engaged means that she has already become a wife. Although an engaged couple have not come together, in the sight of God they are husband and wife.