Great conductors don't do much philosophy during rehearsals. They already have everything clear in their heads regarding what to do and, above all, how to achieve it, and Walter's rehearsals are all illuminating to listen to.
The orchestra is that of Vancouver which, at those times, I believe was not very familiar with the Brahmsian world; seeing in the full version of the video how Walter shapes the sound from a very uncertain beginning to an acceptable and always very musical final coherence is truly fantastic.
A trait of Bruno Walter's that has always fascinated me is how he always manages to bestow upon any orchestra what could be called the "Walter timbre."
Another very important thing is the kindness with which he treats the principals, unlike certain current conductors who "act friendly" to try and ingratiate themselves, masking their true nature from the orchestra.