In terms of Catholic “preachability,” this Sunday’s Readings are a soft-ball pitch, a long high arc that every homilist ought to be able to knock out of the park. The lectionary readings have been set up for a clear explanation of the nature of the Papacy and its basis in Scripture.
The context of the Old Testament reading should be explained. During the lifetime of the prophet Isaiah, the royal steward of the palace, a certain Shebna, was arrogating himself by adopting royal privileges. In particular, he was having a tomb cut for himself in the area reserved for the royal sons of David. Like Denethor in the Return of the King (not an accidental parallel, by the way—Tolkien was a thorough Catholic), he was forgetting his place as steward and confusing his role with that of the king. As a result, the LORD sends an oracle to Shebna via Isaiah, to the effect that Shebna will be replaced in his position by a more righteous man, a certain Eliakim son of Hilkiah: