At-one-ment, the result of Initiation

A point that we need to grasp is that each successive initiation brings about a more complete unification of the personality and the Ego, and on higher levels still, with the Monad. The whole evolution of the human spirit is a progressive at-one-ment. In the at-one-ment between the Ego and the personality lies hid the mystery of the Christian docrine of the Atonement.

One unification takes place at the moment of individualisation, when man becomes a conscious rational entity, in contradistinction to the animals. As evolution proceeds successive at-one-ments occur. At-one-ment on all levels-emotional, intuitional, spiritual and Divine-consists in conscious, continuous functioning. In all cases it is preceded by a burning, theough the medium of the inner fire, and by the destruction, through sacrifice, all of that separates. The approach to unity is through destruction of the lower, and of all that forms a barrier. Take, in illustration, the web that separates the etheric body and the emotional. When that web has been burned away by the inner fire the communication between the bodies of the personality becomes continuous and complete, and the thre lower vehicles function as one.

You have a somewhat analogous situation on the higher levels, though the parallel cannot be pushed to detail. The intuition corresponds to the emotional , and the four higher levels of the mental plane to the etheric. In the destyruction of the causal body at the time of the fourth initiation (called symbolically) "the Crucifixion") you have a process analogous to the burning of the web that leads to the unification of the bodies of the personality. The disintegration  that is a part of the arhat initiation leads to unity between the Ego and the Monad, expressing itself in the Triad. It is the perfect at-one-ment.

First: With himself, and those in incarnation with him.

Second: With his higher Self, and thus with all selves.

Third: With his Spirit, or "Father in Heaven," and thus with all Monads.

Fourth: With the Logos, the Three in One and the One in Three.
Man becomes a conscious human being through the instrumentality of the Lords of the Flame, through Their enduring sacrifice. Man becomes a conscious human being through the instrumentality of the Masters and of the Christ, and through Their sacrifice in taking physical incarnation for the helping of the world. Man unites with the Monad at the fifth initiation, through the instrumentality of the Lord of the World, the Solitary Watcher, the Great Sacrifice. Man becomes one with the Logos through the instrumentality of one about Whom naught may be said.

Reference: Initiation Human and Solar: Alice A. Bailey