The term implies rejection of one way of life for another, generally better, after brief and intense insight into the shortcomings of self or the demands of circumstance. Ancient religious cult did not require such radical or sudden shifts. Devotees could embrace one allegiance without renouncing others. The characteristic word for conversion in the NT, metanoia (change of heart or mind), was used also by Classical philosophers. Acc. to the Stoic Hierocles, ‘conversion is the beginning of philosophy’.
There was among the Romans a contrasting admiration for constantia, ‘steadfastness’, whereby those deserving moral approbation were as likely to maintain the gifts and inclinations of their breeding as to renounce their past in favour of novel commitments.