This quote emphasizes the limitations of human understanding, asserting that our knowledge and reasoning are confined to our experiences and what we have learned. It suggests that whether we’re thinking about divine matters or earthly ones, we can only reason from a position of what we already know.

In the first part of the quote, "Say first, of god above or man below," Pope is establishing two realms of thought: the divine and the human. The divine refers to the spiritual, metaphysical, and unknown, while the human refers to the tangible, physical, and known.

The second part, "what can we reason but from what we know," is a profound observation of our cognitive capabilities. Essentially, it means our ability to think, reason, and understand is heavily reliant on our existing knowledge. We cannot think about something we have absolutely no knowledge of. Our reasoning, therefore, is not limitless but bound by the confines of our knowledge.

Applying this to today’s world, it’s a reminder that our understanding of complex issues – whether they’re scientific, social, or personal – is limited by what we know and understand. This could be seen as a call for humility, a reminder that our perspective is not absolute and can be expanded through learning and experience.

In terms of personal development, it underscores the importance of lifelong learning. To broaden our reasoning, we must strive to learn more. It also suggests that we should be open to other perspectives, as our understanding of the world is inherently limited. Furthermore, it encourages introspection to acknowledge and challenge our knowledge boundaries. It’s a reminder that personal growth comes from pushing these boundaries and expanding our understanding.