Ostara is a celebration of fulfillment! Not that all of the promises made at Samhain have been fulfilled, but a special assurance that they will be. The next celebration, after all, will be of The God/ The Lord coming of age. And this one, we celebrate the fact that he is advancing toward that. In many ancient societies in which child mortality was common, a celebration at this point was appropriate.
And here we also celebrate and make a point of something I keep repeating about because it is so important: fulfillment is a fact! The next Sabbat is Beltaine, and we know when it is going to be - you can mark it on your calendar. And, what is celebrated does not depend on anyone's will, either.