זוהר שמות — דף סט ע”ב

Parashah Yitro. There is no Other Side that does not contain a tiny spark of holiness from the side of Sanctity, like dreams which are mostly straw but contain one grain of wheat. So too on the Other Side, there are sparks of holiness from which the wicked may attempt to draw holiness. This is why Yitro, who came from the Other Side, could hear and receive, because he carried within him a spark of holiness. Dreams are an examination of the human soul and a test of its capacity to receive truth. Most prophecies to the righteous are given unveiled, but to other prophets with a veil.