The Zohar. Chapter “VaYaera (And the Lord Appeared),” Item 424. …The fruit of the actions of the Creator is from that river that stretches out of Eden, meaning ZA and the souls of the righteous. In other words, its deed is the souls of the righteous. And this is the fortune from which all good blessings and timely rains pour out, as it is written, “To water the garden.” It trickles and waters from above downwards because sons depend on this fortune and on no other place….
All our degrees of ascension and correction depend on “fortune” (Mazal) – the Lights that come from above “in drops,” one after another, and seep through the beard of Arich Anpin from his head. And since they come in intervals, we have an opportunity to correct ourselves.
Corrections occur to us step by step, time after time, due to the fact that the Upper Light comes to us in small portions, since a person is incapable of freeing himself from his egoism immediately, in one leap. This is impossible, since egoism is our whole nature!
Therefore, heaviness of the heart comes to us, we overcome it, then it comes again, and we overcome it again, and so on; “drop by drop” we receive correction. All this is due to the revelation of the drops of the Light of Hochma, which are delivered to us by the stream (Zeir Anpin) that flows out of Eden (Bina) and irrigates our souls.
From the 1st part of the Daily Kabbalah Lesson 4/7/10, The Zohar