It honestly depends on who you ask. From what I've ever read it goes like this: The Catholic church, in order to convince people to convert to their religion coopted the holidays and symbols of many pagan celebrations. They then took the various symbols of the old holidays/celebrations and attached them to their "new" god in order to make the transition 'easier' on the people who were newly Catholic. As for the eggs and the bunnies, both things had separate meanings for a pagan festival that happened around the same time of year as Easter, but i have never honestly found any reason for them other than both are symbols of fertility.