Possible meanings are 1) stop speaking, 2) stop speaking when someone is prophesying, or 3) be absolutely silent during the church service.
Paul emphasizes that the Corinthians are not the only ones who understand what God wants Christians to do. AT: "The word of God did not come from you in Corinth; you are not the only people who understand God's will." (See: rc://en/ta/man/translate/figs-rquestion)
"Word of God" here is a metonym for the message from God. AT: "God's message" (See: rc://en/ta/man/translate/figs-metonymy)