The Zohar, Chapter “Lech Lecha (Go Forth),” Item 4: When the Creator created the world, He made the heaven from fire and water, and they were mingled together and did not freeze. Afterward, it froze and stood in the upper Ruach. This is so because in the order of elicitation of the Mochin, first the two lines—right and left—come out. These are the two points—Holam and Shuruk, which are called “water” and “fire.”
The two lines come to us from Above. Indeed, there are only two forces in creation: the Light and the desire to enjoy that it created. It is only when they unite that all of reality is constructed. Hence, the two forces or properties – the Light’s desire to bestow and the vessel’s desire to enjoy – descend to us from Above, from the Creator. Our task is to react to them appropriately through uniting them within us by creating the middle line.
From the 2nd part of the Daily Kabbalah Lesson 7/12/10, The Zohar