why did he write "To A Stranger"?

I do not know Whitman's personal reasons for writing the poem. We can, however, attempt to understand his reasons for writing the poem by interpreting it. The relationship between body and soul is a frequent theme in Whitman's work. Whitman draws on the ideas of Transcendentalism to emphasize the spiritual connection between physical body and nature. "To a Stranger" is similar to Whitman's earlier poem "To You." In both poems, Whitman expresses astonishment at the societal norm of polite reserve between strangers. "To You" questions why it is inappropriate to address a stranger if both parties are willing, but in "To a Stranger" the speaker interprets an unspoken connection with a stranger to mean that they shared a past life. Despite this connection, though, the speaker acknowledges that it would not be proper to directly address the stranger, simply because they are strangers. All he can do is hold onto the hope that their spiritual connection will lead to a physical connection in another life.