God contracted [tzimtzem] His pure light, as it were, just as a father diminishes [metzamtzem] his intelligence and prattles for the sake of his young son. All sorts of other childish qualities are generated in the father, who loves these childish qualities, so that the son may enjoy them, and this is a source of joy to him.
-The Maggid of Mezrich, "Maggid devarav leyaakov" no.1, quoted in N. Lamm, "The religious thought of Hasidism: text and commentary", p. 44.
R' Lamm says the "prattling" refers to prophetic revelation. I thought it meant the simple fact of existing in and experiencing a physical world.