Whitman added material to "Leaves of Grass" and revised the book many times during his life. The most famous poems in the book are "Song of Myself", "I Sing the Body Electric", "Out of the Cradle Endlessly Rocking", and "When Lilacs Last in the Dooryard Bloom'd". The collection praised the human body, the material world, nature, and the experience of the senses at a time when poetry focused on religious experience and the life of the spirit.