“But, that I be not further tedious to you, I entreat you to hear us of your clemency a few words.”
He then assures Felix that his case will not take too long (we probably only have the gist of it) for he does not want to bore him. But he hopes that nevertheless he will listen to him patiently as he will only be saying ‘a few words'. (Felix probably knew from this that he was in for a long, boring peroration).