Baal HaSulam, Shamati #4, “What Is the Reason for the Heaviness One Feels when Annulling before the Creator in the Work”: One must know that he will never come to know the true measure of the importance of the connection between man and the Creator because one cannot assess its true value.
A person has to understand that he will never know the true greatness of the Creator and will not be able to appreciate the real level of connection with Him. In general, he won’t be able to measure anything outside of himself because it is always boundless, while he is capable of perceiving something only in his limited desires (Kelim). Of course, they grow constantly, but they are limited in their capacity.
If now something seems to me as infinite or boundless, it is only with relation to me. For instance, if you fill an 8 ounces glass to the top, it will be infinity with relation to this given vessel (Kli). It’s unlimited and infinite since it received everything!
In other words, everything is measured with relation to desire, a person. If I exist in the state of Infinity on my current level, then later I will reveal an even greater egoistic desire, and I will suddenly discover that I lack everything. But where did my previous state of Infinity go? You sensed it in the desire with the capacity of 8 ounces, but now, when your desire has been expanded to 80 gallons, you do not feel any fulfillment whatsoever.
From the Daily Kabbalah Lesson 12/31/2010, Shamati #4