Why was the Great Invocation not given out until 1945?
The World War, which was drawing to a close in April 1945, had had a profound effect upon the entire planet. The greatest war in human history had caused untold suffering but it had also quite literally blasted open human consciousness as a result of the destruction of old, outworn institutions, habits of living and crystallised thoughtforms that had held humanity in thrall to separatism and materialism, particularly since the time of the Industrial Revolution. The agony of the war and the distress of the entire human family led the Christ, in 1945, to come to a great decision. He made the decision to emerge again into physical contact with humanity if human beings themselves would bring about the initial stages of establishing right human relations; and He gave to the world one of the oldest prayers ever known, but one which hitherto had not been permitted to be used except by the most exalt-ed spiritual Beings. The Christ Himself used the Great Invocation for the first time in June 1945. 
Why is the Great Invocation both a world prayer and an invocation ?
The Great Invocation can be used with special effectiveness by those who have at least some training in meditation. The trained disciple thus can use the Invocation on several levels simultaneously. But the Great Invocation is not a meditation exercise. It is essentially a prayer which synthesises the highest desire, aspiration and spiritual demand of the very soul of humanity itself, and it must be used with that realisation in mind. 
Why does each of the four stanzas refer to humanity ?
In humanity, the fourth and middle, or mediating, kingdom within the range and variety of lives that make up our planet Earth, all lives and aspects of evolutionary development meet. The subhuman kingdoms - animal, vegetable, and mineral - find their consummation and the superhuman kingdoms their opportunity, for through the human kingdom all superhuman lives have passed at some time. The keynote of our planetary Logos, the Lord of the World Whom some call God, is HUMANITY for it is the basis, the goal and the essential inner structure of all being. Humanity itself is the key to all evolutionary processes and to a correct understanding of the divine Plan for our world. All lives are progressing towards the human stage, are presently at the human stage, or have left it behind. The uniformity of experience which this instills makes the art of contact with the divine and the science of impression from divinity possible. Everything that lives on Earth is, has been, or will be human. 
Why does the Great Invocation refer to "men" if all lines of evolution meet in HUMANITY ?
Here a visit to that most occult book, the dictionary, is illuminating. "Man" is from the Sanskrit word manu, meaning "human being", the root of which, man, means "to think". Man thus means "thinking entity" or "one who thinks". This is a highly significant point and one which does not concern sexual gender but rather, that aspect which is common to all members of the human kingdom and that which endows humanity with such a key factor in evolution, the mind. The first stanza of the Great Invocation invokes the Light which originates in the Mind of God - a light which seeks inlet on our planet for the purpose of the redemption of planetary substance through the intercession of the human mind. The mind is what makes man a coherent unit of consciousness, and it is intelligence which is the basis of separativeness. Yet, manas - creative intelligence - is the key to the fifth kingdom in nature: the Hierarchy or Kingdom of Souls. The mind is both a factor of limitation, of separation, and of contact with the inner and higher realms. The mind is a recorder of impressions of all kinds. The primary responsibility of humanity is to act as a major impressing agent in relation to the three subhuman kingdoms - the animal, vegetable, and mineral kingdoms in nature. Humanity's destiny is to be the exponent, the interpreter or representative, of the mind of God. Thus the close relation between the first stanza, which invokes Light from the Mind of God, and the fourth stanza, which invokes the restoration of the divine Plan on Earth through the co-operative effort of humanity. It is the mediating and redemptive role of man, the thinking, light-registering entity, which the Great Invocation addresses. 
Why are the wills of men described as "little" if man's conscious co-operation is needed in order for the Plan to work out on Earth ?
The personal will is that which supports and seeks to sustain the illu-sion in the human being that existence is separate and independent. The personal "little" will endows man with the instinct of self-preservation and self-assertion. The will of the personality is governed by the lower, analytical, form-bound mind, and desire is the emotional counterpart of this will. When the lower mind is brought into contact with the higher abstract mind via the antahkarana-the bridge in consciousness which is created through meditation and service - the human will becomes an agent of the Plan, demonstrating a commitment to serve the Plan at any cost, as that Plan is progressively understood. So profound is the energy of the pure will that only a co-ordinated, consecrated thinker can register and wield it, for the spiritual will is an expression of the Law of Sacrifice.