Final answer:
The phrase alludes to the nature of evil as something invisible to humans and visible only to God, which aligns with the philosophical idea that what we consider evil may actually be part of a necessary greater good, as seen from a divine perspective.
Step-by-step explanation:
The phrase "the only evil that walks / Invisible, except to God alone" appears to refer to the concept of evil as it is understood in a metaphysical or theological context. The quote suggests that evil is something that cannot be seen or fully comprehended by humans, but is visible to the divine perspective or God. According to the philosophical perspective provided by Leibniz, what humans perceive as evil in the world is not inherently evil in itself. Instead, from a divine view, what is considered evil might simply be a necessary part of a greater good or the best of all possible worlds. This notion challenges the human-centric perception of evil and aligns with the idea that our understanding of moral concepts like good and evil is limited by our finite human perspective.
While some traditional views and mythologies personify evil as an independent being or force, this understanding is recontextualized in Leibniz's argument. In this view, the ideas of both "good" and "evil" are human creations and do not necessarily represent an ultimate truth.