In Jewish Law a man betrothed to a woman was considered legally married to her. The word for betrothed in Hebrew is Kiddush, a word that is derived from the Hebrew word Kadash which means "holy" "consecrated," "set apart." Because by betrothal (as in Mt 1:18; Lk 1:27) , or marriage, a woman became the peculiar property of her husband, forbidden to others.
The Oral Law of Kiddushin (Marriages and Engagements) states; "The husband prohibits his wife to the whole world like an object which is dedicated to the Sanctuary" (Kiddushin 2b, Babylonian Talmud).
We know from the Gospel of Matthew 1:14 that Joseph the husband of Mary was a righteous man, a devout law-abiding Jew. Having noticed that Mary was pregnant and that he, her betrothed, had nothing to do with the pregnancy, Joseph had either to publicly condemn her and have her put to death for adultery (Dt 22:22-29) or put her away privately.
His decision was made when an angel appeared to him in a dream, saying: "Joseph, son of David, do not fear to take Mary as your wife; for that which is conceived in her is of the Holy Spirit; she will bear a son, and you shall call His name Jesus, for He will save His people from their sins" (Mt. 1:20-21). The angel does not use the phrase for marital union: "go in unto" (as in Gn 30:3, 4, 16) or "come together" (Mt 1:18) but merely a word meaning leading her into the house as a wife (paralambano gunaika) but not cohabiting with her.
For when the angel revealed to him that Mary was truly the spouse of the Holy Spirit, Joseph could take Mary, his betrothed, into his house as a wife, but he could never have intercourse with her because according to the Law she was forbidden to him for all time.
News to me. Thanks!