To paraphrase a story from Etz Chaim (Tree of Life) by the great Kabbalist Rabbi Isaac Luria, in the beginning God wanted to give, and so vessels were created that could receive God's benevolence. However, these vessels initially could only receive, and in an instant they were filled to capacity and burst. This destruction became known as the shattering of the vessels, the shevirat hakelim. The universe was then reconstituted into a series of vessels that could give as well as receive, and thus, the pressure could now be relieved.
In modern scientific terms, we might think of the shattering of the vessels as the Big Bang, and the reconstituted universe as one in which we live now that is subject to laws of thermodynamics that dictate that energy must flow from a "hot" place to a "cold" place.
At first glance, the universe we live in seems to be inherently unfair. Some places are "hot", filled with abundance, and other places are "cold", void of the bare necessities. However, recall that one of the reasons that the Torah begins with the letter "bet" is to remind us that the universe is a blessing, a bracha. For example, think about a time in your life when you got something you really wanted, and think also about a time in your life when you happened to give someone the exact thing they wanted. Which felt better to you? If you are like me, the joy that came from giving someone even greater than the joy obtained from getting. Because abundance is distributed unevenly throughout the universe, we are able to experience the joy of giving to one another, and through this giving we become a blessing and bring the world back into balance.
If I had to single out one item as the most important lesson that Kabbalah has to teach us, it would be this: that everything in the universe depends upon giving. Kabbalah is not about power or getting rich quick, but about understanding the true nature reality. Part of this understanding is that the existence of everything in this world depends upon there being a constant flow of energy, a continual dance of giving and taking. In particular, to live a life that is healthy and happy, we must keep the flow going at all levels. Physically, we must keep our arteries and veins unimpeded; emotionally, we have a need to both give and receive love; and spiritually, we must give back to the Life of the Worlds through meditation and prayer just as the Life of the Worlds has given to us. To continually give and receive is the most important key to living happily that I have found, and we find this theme reappearing over and over in many forms in the myriad words that have been written on healing by Jews throughout the ages.