Who cares about doctrine?
Levirate marriage was a practice whereby a man was obligated to marry a childless widow of his brother in order to preserve the name and memory of his deceased brother and to ensure the establishment of his deceased brother’s inheritance within the family line (Gen 38:8; Deut 25:5–6). Various forms of this custom were practiced throughout the ancient Near East; in Judaism, Mishnah tractate Yebamoth develops it fully. The practice is first mentioned with reference to Onan (Gen 38:8–10) who, in order to annihilate the line of his brother, refused to have a child by Tamar, wife of his deceased brother Er. Tamar (Gen 38) and Ruth (Ruth 3–4) actually violated prescribed sexual morality to ensure the preservation of their genealogy through levirate marriage. The Book of Tobit tells the story of a woman who married seven men and remained childless (3:7–15)—a story that may have inspired the tale proposed by the Sadducees. The custom of levirate marriage was not devised (as were polygamy and concubinage, for example) for the expressed purpose of allowing a man to have more than one wife, nor to condone sexual promiscuity or immorality. Rather, Levirate marriage was a compensatory social custom designed to prevent intermarriage of Jews and Gentiles and to preserve honor and property within a family line in cases where a woman’s husband was deceased.88
In the minds of the Sadducees, wit and common sense are sufficient to dispel the superstitions of resurrection and life after death. Their question presumes that the world to come is essentially a materialistic extension of earthly life, including the married state, although under more glorious conditions.
The resurrected are immortal, and relationships in that age are different from relationships in this age (on the change in body, see 1 Cor. 15:52).
Those resurrected into new life will be “sons of God” and “sons of the resurrection” (Luke 6:35; Schweizer, TDNT 8:347–49, 355), which is another way to say that they participate in the age to come and have an immortal life (Tiede 1988: 349).
The question is an absurdity, not because resurrection is a problem, but because the Sadducean understanding of resurrection is grounded too much in life as it is now. The afterlife is a different and much greater kind of existence.