This quote speaks to the idea of channeling one’s spiritual or emotional energy into physical, tangible actions. The "surplus life of the soul" refers to the excess of feelings, thoughts, and spiritual experiences that one has. These could be anything – love, anger, inspiration, despair, joy, etc. The "great art of life," as Thoreau puts it, is to translate these abstract experiences into concrete actions that affect the physical world – our bodies and the world we live in.

For example, if you’re feeling a surplus of love and compassion in your soul, you might translate that into physical action by volunteering at a local shelter, helping a friend in need, or simply expressing your feelings to your loved ones. If you’re feeling a surplus of anger or frustration, you might channel that into a passionate speech, a powerful piece of art, or a vigorous workout.

This idea has profound implications for personal development and modern life. In a world that often feels chaotic and overwhelming, it’s easy to get lost in our own thoughts and feelings. We might feel a lot of things deeply, but struggle to express or act on those feelings in a meaningful way. Thoreau’s quote reminds us that our feelings and thoughts aren’t just abstract experiences – they’re a form of energy that can be channeled into concrete actions.

This could mean turning your passion for a cause into tangible action, like starting a charity, organizing a protest, or simply speaking out about it. It could mean channeling your love for a hobby into a career or a side project. It could even mean turning your inner turmoil into a form of self-expression, like writing, painting, or music.

In short, Thoreau’s quote suggests that the key to a fulfilling life is not just to feel deeply, but to use those feelings as fuel for action. It’s about turning the intangible into the tangible, the spiritual into the physical, the soul’s surplus into life for the body.