Imagine that your husband dies and leaves an unmarried brother, or your wife dies and leaves an unmarried sister. If your spouse’s sibling is a Christian, can it be biblical for the two of you to marry?

The Westminster Confession of Faith is one of our “subordinate standards,” the theological documents that define what we believe the Bible teaches but that are themselves subject to scrutiny using the Scriptures. There are a few specific items in the Confession that we reject. One of these is the question of marrying the sibling of a dead spouse. The Confession prohibits it (WCF 24:4), but we believe this prohibition “is not warranted by Scripture” (Testimony 24:22). How did we come to this conclusion?

The medieval Church developed elaborate charts of “consanguinity and affinity,” which were used to determine whether a couple was too closely related to marry. When you married, your spouse’s siblings were deemed to be yours (hence the term “in-law”), and that relationship was considered to be unaffected if your spouse died. Marrying your sister or brother is clearly unbiblical, so it was reasoned that marrying your spouse’s brother or sister is likewise unbiblical.

Early Protestants retained the Catholic prohibition, and the Westminster scholars concluded that it was supported by Leviticus 20:21, “If a man marries his brother’s wife, it is impurity. He has violated the intimacy that belongs to his brother; they will be childless.” They also pointed to Mark 6:18, where John the Baptist condemned Herod II for marrying his sister-in-law Herodias, whom we know from extrabiblical sources had divorced Herod’s yet-living brother.

In 1864, a case of a man marrying his deceased wife’s sister reached the Reformed Presbyterian Synod, which ordered the couple to separate under pain of church discipline. In 1923, Synod quickly turned down a request to study the question, saying the prohibition was clearly supported by Leviticus 18:8–17 and 20:21. In 1947, Synod partially reversed course by appointing a three-elder study committee.

After reviewing the biblical texts and multiple commentaries, the committee urged a change in the church’s position. One popular commentary concluded that Leviticus 18:18 was irrelevant because Hebrew uses “sister” to mean many kinds of female relatives, and the passage prohibited polygamy. This position they rejected because the rest of the chapter is related to incest. However, they followed the scholarly Keil-Delitzsch commentary’s opinion of this passage: because the passage prohibits being married simultaneously to two sisters, it refers to situations such as Jacob’s simultaneous marriage to Rachel and Leah, which interfered with the sisterly relationship. Consequently, they followed the commentary in concluding that this passage placed no restrictions on a widower marrying his wife’s sister, since the latter marriage was not in the first wife’s lifetime.

The elders also looked at the “levirate marriage” law of Deuteronomy 25, which directed a single man to marry his childless brother’s widow. Following the principle that unclear parts of the Bible are to be interpreted by clear parts of the Bible, the committee’s argument focused on levirate marriage. Because the Bible commanded a man to marry his dead wife’s sister, and because the Bible cannot require us to do evil that good may result, they concluded that such a marriage was not prohibited by Leviticus 18.

Synod was persuaded by their argument and adopted their report as its position. Some elders dissented, but they mostly focused on the procedure; their only reference to biblical teaching was a statement that sister-in-law marriage was forbidden “by the whole chapter [Leviticus 18] and by other passages of Scripture” without need for the Hebrew exegesis undertaken by the committee. No response to the levirate marriage question was made. Ultimately, our Testimony was updated in 1950 to reflect the new position, and thus we disagree with Westminster on this point.

To answer the question: yes, it can be biblical. Is it the right thing to do? That depends on the circumstances. Ask your session for counsel!