Because the weekly schedule covers many chapters, the pulpit ministry will probably only focus on a particular passage or just a few points or themes. Attempting to provide a more general overview of the entire week’s reading should be the focus of Adult Sunday School.
Having encouraged attenders to do the reading the week leading into each Sunday School lesson, this is the place people should be encouraged to bring any general questions and where an overview is given to help everyone place the reading in the right historical and theological context.
This is the time to go over maps, the meaning of names, the timeline of Israel’s or the early church’s history, and so on, to provide a framework. It’s great that a whole congregation reads the entire book of Isaiah, and even receives specific teaching on it from the pulpit, but the context of Isaiah’s ministry, the setting for God’s words, the historical events in parallel with his ministry are crucial to making the reading understandable and even enjoyable at all levels.
Consider that you may not necessarily need a seminary graduate to teach Sunday School in this manner because the local Bible book store is bursting with books, lesson plans, etc. It may simply be a matter of choosing materials that parallel the reading schedule. The various study aids available for download from Walk with the Word are oriented to address this need as well.