To Do What is Really Right

Why would the same garments be a merit in one place and a command in another? In Parshas Bo, Bnei Yisrael are saved in the merit of not changing their clothing, yet Hashem tells them to take clothing from the Egyptians. Three yeshiva boys, a popular band, and a Rosh Yeshiva who gives an ultimatum over something that was perfectly permitted bring the question close to home. Why would a Rosh Yeshiva care so much? It reaches every choice we make about things that are allowed.