Deuteronomy 25:5-10 addresses a statute that had unique application to ancient Israel. Now called the law of levirate marriage, from the Latin word levir, meaning "brother-in-law," it stated that if a married man died without children, his widow was to be married to his brother (her brother-in-law), or his nearest of kin if there was no brother, and the first child of this new union was to be regarded as the offspring of the deceased husband (compare Genesis 38:9; Matthew 22:24).
This was to be done so that the name of the dead brother would "not be blotted out of Israel." It also ensured that the widow would continue to be provided for. Obviously, then, this could have put certain economic strain on the levir, particularly if he already had a family, as he had to provide for a wife and for the raising of a child until that child was old enough and independent enough to carry on the name of his "father" on his own. The nearest of kin could, however, refuse to take the widow as his wife, although he would have to go through a humiliating process in which everyone saw his selfishness in being more concerned for himself than for his extended family (verses 9-10). In the case of Ruth in the biblical book bearing her name, her deceased husband's closest relative refused to marry her, so that Boaz, the next in line on the kinship list, was free to do so (Ruth 3:13; Ruth 4:1-9).
The law of levirate marriage is not applicable in the Church today. One reason is that a literal application of it would often require a converted brother-in-law to marry an unconverted sister-in-law, or vice versa, which would be contrary to 1 Corinthians 7:39 and 2 Corinthians 6:14. Also, if the brother-in-law were already married, the application of this law would violate the biblical teaching (discussed earlier) that a man is to be the husband of only one wife. As this is specifically mandated in the New Testament for ministers and deacons, it is understood to be binding upon all men in the Church.