The Buddha delineated four successive stages of awakening. We don’t have to awaken all at once, so it’s not too overwhelming…Maybe some people do have an instant or spontaneous awakening, but I think that even if they do, that experience still requires a certain development and filling out.
One can have moments of clarity and glimpses of truth, but unless the experience becomes really grounded in our whole being, it’s just a flash of insight and that’s about it. It’s like when we wake up in the morning. We can have an ‘insight’ into how the day might be, but then we need to build our life around it. So even if we have an ‘awakening experience’, we still need to integrate it into spiritual practice, put it into our life and live it.
The Buddha’s graduated teaching on the four stages of awakening is one way of giving people something practical to which they can relate. They can recognize that they are changing. Certain fetters, certain disturbances, certain ways of relating are gradually relinquished.
This reflection by Ajahn Thiradhammo is from the book, Contemplations on the Seven Factors of Awakening,
(pdf) pp. 133, 134.