Why is Bernard's announcement of his engagement in Section 4 significant?

The announcement is significant for two reasons. First, it shocks the group into recognizing that Bernard, the novel's most central character (though none of the characters are the most important), has made a decision to remove himself from the group. Secondly, it is significant because of the timing as they gather before Percival leaves for India. Rather than announcing the engagement, Bernard announces it when the group feels closest, albeit a fleeting sensation.