Michael Tilson Thomas was looking hard for insight in Schubert last Saturday. He found it in words, if not in the music. Indeed, you might say he chose the first Entr'acte from Rosamunde for an illustration of his point. As a young man, Thomas managed to alienate the Boston Symphony for decades by talking too much, and the tendency to lecture and otherwise condescend to his audiences from the podium still remains. This time, though, the music happened to be rather forgettable, and Thomas' remarks about it more interesting. The Entr'acte seems to be part of a dry run for Schubert's "Unfinished," and MTT correctly pointed out that its harmony is headed in the direction of Mendelssohn and Schumann.