I have previously written an article about 1 Peter 3:7, the Bible verse that includes the phrase “a weaker vessel” [here]. Since writing this article, however, I’ve come across a few references in Greek papyri where women are called “weak” (asthenēs). In these papyri, women use the adjective for themselves hoping to elicit pity, or hoping to ingratiate themselves, while seeking justice from men. A.L. Connolly comments on several of these legal petitions and notes that appealing to a woman’s frailty (asthenēs) “had become commonplace in the rhetoric of petitions.”
Peter calls wives “weaker vessels” because he wants husbands, not necessarily to pity them, but to be more understanding with their wives. Ancient women were, with few exceptions, disadvantaged economically, legally, and politically. However, the Greek word asthenēs is used many times in the New Testament to mean weak, sick and infirm. So physical weakness may be what Peter had in mind.
Interestingly, Paul (who readily admitted to his own weakness) used the word asthenēs (“weak”) many times in his letters. He used it eleven times in First Corinthians, including 1 Corinthians 1:27b where he wrote, “God chose what is weak in the world to shame the strong.” Paul used the comparative form of asthenēs (= “weaker”) in 1 Corinthians 12:22 where he wrote, “the members of the body that seem to be weaker are indispensable.” Peter likewise uses the comparative form of asthenēs (=”weaker”) in 1 Peter 3:7.
Physical weakness is not a disadvantage in the body of Christ, and it need not be a disadvantage in marriage.
Neither Peter or Paul use the word “weaker” to insult or diminish anyone. In fact, they do the opposite. Like the women seeking justice, Peter uses the word “weaker” for its rhetorical effect, and he juxtaposes the phrase “weaker vessel” with the phrase “bestowing honour”.
It was not unusual to hear women being called “weak” or “weaker” in the first century. On the other hand, many may have been surprised to hear Peter tell husbands to honour their wives. Furthermore, Peter gives the reason why husbands should honour their wives: because a Christian couple are co-heirs of “God’s gift of new life” (1 Pet. 3:7 NLT). Being co-heirs is a strong basis for mutuality and equality in marriage.
I’m not bothered that Peter called wives “weaker”, considering it was part of the rhetoric of petitions. Moreover, I’m delighted that he appealed to husbands to treat their wives with honour and understanding, and to acknowledge them as co-heirs. It seems Peter was advocating for justice in marriage.
 “30. ‘The Weaker Sex'”, G.H.R. Horsley with A.L. Connolly, New Documents Illustrating Early Christianity: A Review of the Greek Inscriptions and Papyri in 1979, Volume 4 (The Ancient History Documentary Research Centre, Macquarie University, 1987), 131-133, 132.
 The entry on asthenēs in the LSJ Greek-English Lexicon is here. It gives the primary meanings as “without strength” and “weak”, and lists other kinds of weaknesses, not just physical or bodily weakness.
 Note that Peter does not say that women are “weak”. Rather, his meaning is that wives are “weak-er” than their husbands.
 Peter writes that the Christians in Asia Minor should also honour the emperor (1 Pet. 2:17).
Submission and Respect from Wives in 1 Peter 3:1-6
Submission and Respect from Husbands in 1 Peter 3:7-8
Fear or Respect in Christian Marriage?
Equality and Unity in Ministry in 1 Corinthians 12
Protecting the Weaker Sex