The accusation in this verse is that Christians have taken the Messiah as Lord ( rabb ). This is accurate. The New Testament says, “If you confess with your mouth, ‘Jesus is Lord,’ and believe in your heart that God raised him from the dead, you will be saved” (Romans 10:9). The Quran’s issue with the term rabb is that it implies the deity of Jesus and his supreme authority to command humanity how to live. See the analysis of the Quran’s denials of the deity of ‘Īsā at 43.59.

Verse 31 continues with the words “they were only commanded to serve one God. (There is) no god but Him” – a statement very close to the first part of the Muslim confession of faith. Here again the Quran says that Christians are “associating” ( ashraka , also v. 33; see the comment at 9.5). The Quran contains characterizations of Christians, Jews, and others that almost none of the followers of those faiths would give. See a summary of verses that accuse the People of the Book of “associating” at 61.9.