In Kabala, there are four Olamot (worlds). This physical world is the lowest and is called Asiyah. The next higher world is called Yetzirah. In each higher world the unity with G-d is greater, to the point where in the highest world nothing is discernible as being outside of G-d. Our prayers correspond to the four levels - the physical (Asiyah) is when we recite the sacrifices, Yetzirah is when we read the Psalms of praise to G-d, Beriah is our recital of the Shema and its blessing, some concepts involved include willingness to sacrificing our life, acceptance of the yoke of Torah, and reminders of Egypt. Finally, when we recite Shemoneh Esrei, our entire being is represented as indiscernible from G-d because all of our requests , all that which makes up our being, are to Him and blessings of Him. On that level we are more intertwined with G-d, more indiscernible from G-d.
- Based on Rabbi Reisman of Madison's shiur April 17, 1999
The Maharal asks why when referring to these four we use the term Worlds rather than Levels. The answer is that like a world, a person cannot be in one at the same time as another. Prior to Adam's sin, it was normal to be in more than one world at one time, but in post-sin fallen from Eden existence, the general rule is to be in one world at a time. The functional meaning of this concept is that our decisions are dependent on whichever world we are living in.
For instance, if a person hits you, it hurts in Asiyah, the lowest world, because it causes physical pain. In Yetzirah, a spiritual world, it hurts because it was unjust for the person to hit you. If someone hits your friend, then, it will still hurt, only this time it only hurts on the Yetzirah level. If your response is the same whether your friend is hurt or you are hurt, you are functioning more in the Yetzirah level.
Harnessing your desires is a great way to serve G-d, and transforming your sensitivity is even greater. On the other side, failure to serve G-d by doing sins motivated by desire for pleasure is not good, but on another level is where a person thinks he knows better than G-d and therefore he transgresses the Divine Command. There is a level called Yetzirah where things that don't make sense in this world are true. We are born with a sensitivity to those things. That is how Abraham, Isaac and Jacob were able to observe the Torah before it was given.
When we live in this physical world, not being the great Patriarchs, it is very easy for us to transgress what is true in the higher worlds, because it doesn't make any sense here. It doesn't make any sense for a business to close on Shabbos, or for a person to wear Tefillin, in terms of advancing one's standing in this physical world, and in fact most successful corporationsare those that are not observant of mitzvot (commandments). But on the Yetzirah level, decisions of what to do in the physical world is seen as whether or not it advances what is true on that spiritual realm. Are the employees and customers treated according to business laws in the Torah?
The basis of marriage is a committment to do what is true in higher realms, and when people lose sight of that their marriages are in jeopardy. A man told a therapist he had marital problems, so the therapist said to run 10 miles a day to ease the tension at home. The therapist said to call back in two weeks to say how it was going. So two weeks later, the man called the therapist and said that he had been running ten miles a day, and it was working great. "And what does your wife say?" asked the therapist. The man answered, "How should I know - she's 140 miles away from here."
The mussar approach to dealing with marital crisis is different and simply based on the idea of doing what we would do if we were in love, act "as if", and continue to do so until the feelings of love come back. This approach is more based on the world of Yetzirah. Love in the relationship is a concept that the players will be sensitive to regardless of what's going on in this physical world, if they will let that sensitivity come into play. The crisis is in this physical world and is temporary, so the marriage can survive.
The masters of mussar used to go to a courtroom before Rosh Hashana - they wanted to see in this physical world the people who were afraid of being judged. One reason why going to a cemetary is so beneficial is that it is a physical representation that reminds us that this world is not the only world and in this life there is a finite time in which we can prepare for the eternal world. These practices are based on the idea that we admit that we live in the lowest physical world. Nevertheless, we are capable of accepting that the Torah, Prophets and Sages have given us teachings, laws and customs that recognize the higher worlds and operate in the lower world to expose ourselves to those things that promote what is true in a higher world.
Chassidic masters discuss the different worlds at length, and seem to attempt to describe the bliss one would find if he were able to transform not only his desires, but his sensitivities themselves. For instance, in Likutei Dibburim, available in English, by Rabbi Yosef Yitzchak Shneersohn, at the end of Book One there is a description of a Rebbe discussing these concepts to a Chassid.
With all the examples given, physical pain, the Patriarchs, business, marriage, and development of one's sensitivities, we can now see the Maharal's question of why the worlds are called worlds and not levels. The word "world" is stronger than "level." Let's say a person is standing on a staircase, which has many levels. If he sees a roller skates blocking another step, he almost effortlessly gets off his step, and goes up or down a few levels to remove the obstacle on another level. However, if we are in one world and the blockage is in another world, we cannot so easily leave our world in order to fix what is wrong or improve things in another world. If astronomers detected that planet Neptune was going to blow up, what do you think the first question would be? Is it good for Neptune? No! The first question would be whether the pieces of Neptune will hit Earth, and in what other ways might Earth be impacted. It is impossible to be in two worlds at once, and it is impractical to think that in the moment we really consider what is good in another world. It is to point out to us that if we are influenced and "living" in one world, we are only sensitive to the other world in a relative way.