Part of my secular background is in teaching, so I've been doing a good bit of informational preaching. I've noticed that there is a lot of biblical illiteracy in general...even the very, very basic stuff. Fortunately, while many United Methodists do use the lectionary, we aren't forced to use it, so even when I do start off with a single lectionary text, it can turn into multiple sermons, especially when writers like Paul or the author of Hebrews, etc. assumes cultural knowledge of his time that we don't have. How many people, for example, could even point out where the city of Ephesus was on the map (or know it was located in modern day Turkey vs. everything being in "Israel" or the generic "Middle East", or may have even heard of it to begin with, despite a book of the bible being called Ephesians?
The author of Hebrews was very likely writing to a Jewish Christian audience, so assumes a lot of familiarity with old testament scriptures, which many people today often don't have.
This past week, I was focusing on Hebrews 4:14-15 about Jesus being our high priest and so went back to the time of Moses and Aaron and how the Israelite high priesthood was formed and what happened on the Day of Atonement (and even what the word "atonement" even means), etc. If people don't have this background, they aren't going to more fully understand what it means for Jesus to be our high priest and how his being our high priest helps us today. In fact, many Methodists don't even really know what a "priest" is because we don't have them (despite the Wesleys having been Anglican priests), and there is a difference, at least historically, between a priest and a pastor, preacher, minister, etc.
Should *all* our sermons be of just one type? Nope, of course not, but I don't think we need to neglect informational teaching, especially in smaller congregations that may not have a formal bible study or Sunday School time.
If people don't even know who Paul was, then they may not care what Paul has to say despite him being some guy "in the bible".