The Book of Zohar, “Two Points,” Item 121: …Thus, the locks, the doors, and the halls are three forms that come upon our substance, the desire to receive in us. Before we turn it into reception in order to bestow upon our Maker, that substance turns the light to darkness and the sweet to bitter, according to our taste… .
It is actually our intention of in order to receive that turns the sweetness into bitterness and we feel bitterness. When we correct the intention, the bitterness becomes sweet. This means that everything depends on the equivalence of form between us and what comes from Above. To the extent that we have an intention of in order to bestow, everything can be felt as sweet and above this intention everything is felt as bitter since I have nothing to sweeten it with.
It is the intention that makes everything bitter or sweet. There is nothing but the intention, and we don’t need to work with anything but the intention. Leave your desires and your attributes alone, they don’t matter. We already know from our experience that a person remains with what he is born with. Nothing changes in him except for one thing. Therefore, we only worry about the intention, about our attitude towards the Creator.
From the 3rd part of the Daily Kabbalah Lesson 1/13/14, Writings of Baal HaSulam, “Introduction to the The Book of Zohar“