Why do we celebrate becoming free at the exodus, given that we have since been subjugated again? At the exodus, the Jewish people acquired their essential identity as free people. This is therefore a dramatic event for all generations.

When the Israelites left Egypt they received essential goodness until they were inherently fit to be free. This is the essential nature of Israel, that they are fit to be free people in their very essence. That which is incidental can never negate that which is essential. The Jewish people retain this quality of being free people in their essential nature, despite occasional subjugation. (Maharal, Gevurot HaShem 61)