"As I get older I seem to believe less and less and yet to believe what I do believe more and more"

This quote by Gerald Brenan talks to the concept that as we age, our beliefs end up being more focused and more deeply held. As we get experience and knowledge, we end up being more aware of what we believe and why we believe it. We might come to understand that some of our beliefs are unproven or misguided, and so we might discard them. At the exact same time, we might become more certain of the beliefs that we do hold, and so we may become more enthusiastic and committed to them. This quote suggests that as we age, we become more discerning and more positive in our beliefs.