The meaning of and

?“Of course, there is a portion of reading quite indispensable to a wise man. History and exact science he must learn by laborious reading. Colleges, in like manner, have their indispensable office, - to teach elements. But they can only highly serve us, when they aim not to drill, but to create; when they gather from far every ray of various genius to their hospitable halls, and, by the concentrated fires, set the hearts of their youth on flame. Thought and knowledge are natures in which apparatus and pretension avail nothing. Gowns, and pecuniary foundations, though of towns of gold, can never countervail the least sentence or syllable of wit. Forget this, and our American colleges will recede in their public importance, whilst they grow richer every year.”

1. In the last sentence "forget this...year", does "and" mean "as a result"?
2. In the last senrence, does "and" sound sarcasric?

3. As a side question, why is there "-" between office and to teach elements in the third line? Was is used to make "to teach elements" modify "their indispemsable office"?

4. If 4 is correct, does "to teach elements" not mean "in order to teach elements"?