Deuteronomy 25:6
And it shall be, that the firstborn which she beareth shall succeed in the name of his brother which is dead, that his name be not put out of Israel.
Cross-reference
Ruth 4:1–7
Historical context
Ruth 4:1-7 narrates the legal proceedings for redemption and marriage, executing the levirate duty prescribed in Deuteronomy 25:6.
Ruth 4:10–12
Prophetic fulfillment
Ruth 4:10-12 is the climactic fulfillment: Boaz raises up the name of the dead, directly enacting the law of Deuteronomy 25:6.
Genesis 38:9
Parallel
In Genesis 38:9, Onan's refusal to give offspring to his brother directly violates this levirate duty, illustrating the principle in action.
Ruth 4:5
Allusion
Ruth 4:5 has Boaz explain that redeeming the land includes marrying Ruth to perpetuate the dead's name, directly echoing this law.
Matthew 14:4
Contrast
Matthew 14:4 shows John condemning Herod for marrying his brother's wife while he still lives, contrasting this law which only permits it after death.