In Walt Whitman's "Song of Myself," there are many aspects to ponder, but the one that strikes me is that of universality.
Whitman notes that he is one with nature, one with all the men and women ever born. Life is a cycle, where mankind does the same things over and over again, through the generations. Some things are known and can be explained, and some not. But Whitman seems to have faith that he fits in as he is, despite what others see in him, despite how others act. Whitman knows that there are things he cannot pretend to fully understand, even the most simple concepts: as when the child asks him 'what is grass?'
Whitman seems content in the time he has, hoping for health for the length of his life, and believing in the cylcles: life and death, and that they are both to be expected.
Whitman makes mention of many aspects of society at his time. He sees himself sometimes as his own worst enemy, but still he comes back to nature. He speaks of fighting, of disease, of religion. He addresses society and its many members.
The poet sees himself as one of many, but still one on his own journey. Every man has his own journey that no one can complete for him. Whitman describes himself only as a teacher. His own value he finds in the value of others. He encourages others to lean upon him, and that one day they will be there so that he may lean upon them.
And then Whitman speaks of Death and that journey that waits for him. He is a part of the world and nature. He is connected with nature, but also with all of mankind. He takes his lot in life as it comes, contented to take his place among others in the world to do what he may, but there is the constant reference to oneness, and all things—himself included—connected to all other things. He is a part of the whole. He is one: but he is all. In these instances, the reader sees Whitman's sense of universality.