So you wouldn't have been certain of the oral preaching of Sts. Peter and Paul or the other apostles unless they wrote it down.<quoted text>
Oh but it is less valuable as we see here;
3Therefore, since I myself have carefully investigated everything from the beginning, it seemed good also to me to write an orderly account for you, most excellent Theophilus, 4so that you may know the certainty of the things you have been taught.
To be 'Certain' we go with what is Written.
Actually, I think think the only preaching you're certain of is your own. Quit drinking the bong water marge.