"Now I beseech you, brethren" (1 Corinthians 1:10): sounds like Paul is addressing only the men in the church

1 Corinthians 1:10 opens, "Now I beseech you, brethren, by the name of our Lord Jesus Christ, that ye all speak the same thing." To modern English ears, "brethren" sounds like it's speaking to the male members only, since "brother" today means a male sibling, full stop. But the underlying Greek word, adelphoi, functioned in first-century usage as the standard plural for a mixed group, and Paul plainly has the whole church in view here, since he goes on discussing women praying and prophesying just two chapters later (1 Corinthians 11).

This is exactly why modern translations like the NIV and CSB now render adelphoi as "brothers and sisters" in these congregational addresses. The KJV isn't wrong so much as dated: "brethren" was a fine stand-in for a gender-inclusive term in 1611, but English "brethren" has since drifted to sound exclusively male, misleading readers about who Paul was actually talking to.