Hearts doubtless warmed upon the first reading of the opening of all Paul's letters in the various churches, even the screw-ups in Corinth, upon whom Paul heaped admiration and joy--all, that is, except the Galatians. 'I am astonished that you are so quickly deserting . . .' (Gal 1:6) What would it have been like to be there? James Dunn is right:
The atmosphere in the congregations in Galatia when the letter was first read out to them must have been electric. Their own astonishment and upset at the charges already levelled against them would ensure careful attention to and careful scrutiny of what he was about to say. The tactic was no doubt deliberate.
--Galatians (BNTC, 1993), 51