Definition and Origin:
Levirate marriage is a practice rooted in ancient Near Eastern customs, where a man is obligated to marry his deceased brother's widow if the brother died without leaving a male heir. The term "levirate" is derived from the Latin word "levir," meaning "brother-in-law." This practice is primarily outlined in the Hebrew Bible and serves to preserve the family lineage and inheritance within the tribe of Israel.

Biblical Foundation:
The concept of levirate marriage is explicitly detailed in the Old Testament, particularly in the Book of Deuteronomy. Deuteronomy 25:5-6 states: "If brothers dwell together and one of them dies without having a son, the widow must not marry outside the family. Her husband’s brother is to take her as his wife and fulfill the duty of a brother-in-law to her. The first son she bears will carry on the name of the dead brother, so that his name will not be blotted out from Israel."

This passage underscores the importance of maintaining the deceased brother's name and property within the family, ensuring that his lineage and inheritance are preserved.

Cultural and Theological Significance:
Levirate marriage was not merely a familial obligation but also a social and theological duty. It was a means to protect the widow from destitution and to ensure that the deceased brother's name and estate remained intact within the tribal community. This practice reflects the communal and covenantal nature of Israelite society, where family and tribal continuity were paramount.

Theologically, levirate marriage can be seen as a reflection of God's concern for the vulnerable, particularly widows, and His provision for the continuation of His people. It also highlights the importance of family and inheritance in the biblical narrative, themes that are recurrent throughout Scripture.

Examples in Scripture:
One of the most notable examples of levirate marriage is found in the account of Tamar and Judah in Genesis 38. Tamar, the widow of Judah's son Er, is denied the levirate marriage by Judah's second son, Onan, who refuses to fulfill his duty. This leads to a series of events where Tamar takes matters into her own hands to secure her place and the continuation of her deceased husband's line.

Another significant example is the account of Ruth and Boaz in the Book of Ruth. Although not a direct levirate marriage, the narrative reflects similar principles. Boaz acts as a kinsman-redeemer, marrying Ruth, the widow of Mahlon, to preserve the family line and inheritance.

Legal and Social Implications:
The practice of levirate marriage had specific legal implications within the Israelite community. If a man refused to marry his brother's widow, the widow had the right to publicly challenge him. Deuteronomy 25:7-10 describes the procedure: "But if the man does not want to marry his brother’s widow, she is to go to the elders at the city gate and declare, 'My husband’s brother refuses to preserve his brother’s name in Israel. He is not willing to perform the duty of a brother-in-law for me.' Then the elders of his city shall summon him and speak with him. If he persists and says, 'I do not want to marry her,' his brother’s widow shall go up to him in the presence of the elders, remove his sandal from his foot, spit in his face, and declare, 'This is what is done to the man who will not build up his brother’s house.' And his family name in Israel will be called 'The House of the Unsandaled.'"

This public act of removing the sandal and spitting in the face served as a form of social censure, emphasizing the communal responsibility to uphold family obligations.

New Testament Context:
In the New Testament, the concept of levirate marriage is referenced in the context of a theological debate between Jesus and the Sadducees. In Matthew 22:23-28 , the Sadducees present a hypothetical scenario involving levirate marriage to question the resurrection. Jesus uses this opportunity to teach about the nature of life after resurrection, indicating that earthly institutions like marriage do not apply in the same way in the afterlife.

Conclusion:
Levirate marriage, as depicted in the Bible, is a complex institution that intertwines legal, social, and theological elements. It reflects the ancient Israelite values of family continuity, social responsibility, and care for the vulnerable, while also providing a framework for understanding certain biblical narratives and teachings.