What does the speaker compare life to in the first stanza of James Russell Lowell's "Life"?

In the first stanza of James Russel Lowell's poem 'Life', the speaker compares life to a leaf of white paper where each one of us may write. What the author was trying to say is that each living person has the same opportunity at birth, that is, we all have life, what we choose to do with our lives is the information that we put on the white paper.