A quote from Martin Buber on why he wrote his “ideas” about life in poetic form rather than as doctrine (most of the existentialist did the same, but also the religions!):

Poetry and art invite “encounter”. Unlike a doctrine which only addresses the mind, a poem or piece of art addresses more of the whole person, and engages it in order to “know” it.
Even the Bible (which Buber translated into German) is written broadly in stories and poetry, riddles and parables which invite us to encounter the reality of what it is trying to say. There are commandments on stone, but they are embedded in a story, and engraved in a people’s heart.The bible is not presented as a list of principles, it is rather an invitation to encounter the essence of its principles. This is done through art.
Life is an invitation, not a mere set of ideals. Life is meant to be actually lived that is. Encounter in wonder, love and thanks, in order to know what life is.