The middle class gospel says this:
I'm basically good and I can sort out my life by making free choices and working hard.
But Jesus said that to be saved we must be poor in spirit. In other words, we may be outwardly wealthy, but we must become like the poor if we are to be saved.
In other words:
I'm not basically good. I can't just sort out my life by trying hard. I don't have the power and there are lots of things that enslave me. I need a Saviour to come and rescue me.
The poor teach us the gospel and this is why the gospel is for the poor. The rich can only access it by becoming like them, by realizing their need of Another's spiritual wealth to help them.