There really was no middle class in the Palestinian territories at the time. There was a tiny, elite and aristocratic class and there was the vast majority who were peasants. There was no vertical mobility between those classes, and the economic system was based on gross exploitation of the lower classes. Farmers worked on land owned by wealthy landlords for bare subsistence. Fishermen on the Sea of Galilee had to pay for a spot on the lake to fish in then turn over most of what they caught.

A lot of what Jesus is depicted as preaching is that there would be a reversal of the social order, that the "first would be last and the last would be first," etc. So he was talking about a class, not a tax bracket.

On another level it can be argued that he was saying material desires are simply incompatible with spiritual progress. "Do not store treasures on Earth." and so forth.