I have described myself as always having been imbued with a fervent longing to penetrate the secrets of nature.
In this line, the author is exploring man versus nature. The word or phrase from this passage that best demonstrated the conflict between man and nature is perhaps ‘penetrate’ or specifically ‘penetrate the secrets of nature’.
‘Penetrate’ means to succeed in forcing a way into or through. This signifies that the persona in this passage wants to understand the mysteries that surround nature.