The Buddha's Enlightenment is the central event in Buddhism, and the celebration of that Enlightenment is an important event in the Buddhist year.
Enlightenment is also an ideal to which all Buddhists aspire and on this evening we will celebrate the life of the Buddha with a devotional Puja.
Puja is about the cultivation and expansion of positive emotions including shraddha (faith-confidence). It is a practice which helps us crawl in behind the limited, habitual, fixed self and for a time experience ourselves as much more expanded and limitless.
Sangharakshita describes shraddha as a lifting up of the heart to something higher, touching something higher, experiencing, even if only for a moment, something higher. When we do this with one another it deepens the development of true community so that Sangha can indeed become a real and abiding refuge.