The created being must be between two systems in order to grow and to exist: the shell (Klipa) and holiness (Kedusha). This is why there are the worlds of ABYA of holiness and ABYA of impurity, as it it is said, “God has created them one opposite the other.” The souls are in the middle and as they go through the phases of development, they are alternately influenced by the system of purity and the system of impurity.
Accordingly, those who are nourished by the system of the Klipa are called dead and those who are nourished by holiness are called alive. Thus the influence of the worlds helps the souls develop continuously between life and death.
We gradually develop from the simple desire to live a material, corporeal life into a desire of a spiritual level. On this level there is no more life and death in the usual sense. In the spiritual life we are independent of the body; we rise above it and begin to feel a different level of life. Then life means that we are under the influence of the force of bestowal and death means that we are under the influence of the force of receiving.
This teaches us how to turn all the forces from the intention of in order to receive, from the evil inclination, to the good inclination. Thus we establish our spiritual life.
We must understand what the principle of “God created them one opposite the other” means here: If one desire is evoked in us, the other desire falls, and vice versa. The two systems cannot operate simultaneously. The effectiveness of one system is at the expense the ineffectiveness of the other system. Thus they operate alternately, according to the upper plan that is in the world of Atzilut.
The systems of BYA of holiness and BYA of impurity help us advance by pushing us forward. If we advance by the system of BYA of impurity, we develop “in its time,” and if we advance by the system of BYA of Holiness, we hasten our development, which is called “I shall hasten it.”
From the 2nd part of the Daily Kabbalah Lesson 01/01/14, Writings of Baal HaSulam