Egg-shells and Rabbit Liver

I've been reading Dietrich Bonhoeffer's Letters and Paper's From Prison for my Modern European Literature class. I've enjoyed our class discussion so far, but I'm afraid much of the reading goes over my head. I get bogged down in passages like this:

Barth was the first to realize the mistake that all these attempts (which were all, in fact, still sailing, though unintentionally, in the channel of liberal theology) were making in leaving clear a space for religion in the world or against the world. He brought in against religion the God of Jesus Christ, 'pneuma against sarx'. That remains his greatest service (his Epistle to the Romans, second edition, in spite of all the neo-Kantian egg-shells). Through his later dogmatics, he enabled the church to effect this distinction, in principle, all along the line. It was not in ethics, as is often said, that he subsequently failed - his ethical observations, as far as they exist, are just as important as his dogmatic ones -; it was that in the non-religious interpretations of theological concepts he gave no concrete guidance, either in dogmatics or in ethics. There lies his limitation, and because of it his theology of revelation has become positivist, a 'positivism of revelation', as I put it.

Is there anyone who would care to explain that to me in layman's terms, in case Dr. Lundin doesn't get to it? I would particularly like to know about Neo-Kantian egg-shells.

There are bits that I find more interesting, even entertaining. These couple sentences in particular caught my attention:

I was very touched when the Schleichers sent me the rabbit liver a little while ago. A real piece of meat is very welcome in all this spoon-fodder.

All of a sudden my appreciation for SAGA multiplies tenfold.
But I doubt that I could write a good paper on that observation.