What is the origin of Urantia book?

The origin of the Urantia Revelations is in the RED highlighted text below. A promise made by Jesus.

^176:2.3 In further answer to Peter's question, Jesus said: "Why do you still look for the Son of Man to sit upon the throne of David and expect that the material dreams of the Jews will be fulfilled? Have I not told you all these years that my kingdom is not of this world? The things which you now look down upon are coming to an end, but this will be a new beginning out of which the gospel of the kingdom will go to all the world and this salvation will spread to all peoples. And when the kingdom shall have come to its full fruition, be assured that the Father in heaven will not fail to visit you with an enlarged revelation of truth and an enhanced demonstration of righteousness, (5th Epochal Revelation) even as he has already bestowed upon this world him who became the prince of darkness (1st Epochal Revelation), and then Adam, (2nd Epochal Revelation) who was followed by Melchizedek,(3rd Epochal Revelation) and in these days, the Son of Man.(4th epochal Revelation) And so will my Father continue to manifest his mercy and show forth his love, even to this dark and evil world. So also will I, after my Father has invested me with all power and authority, continue to follow your fortunes and to guide in the affairs of the kingdom by the presence of my spirit, who shall shortly be poured out upon all flesh. Even though I shall thus be present with you in spirit, I also promise that I will sometime return to this world, where I have lived this life in the flesh and achieved the experience of simultaneously revealing God to man and leading man to God. Very soon must I leave you and take up the work the Father has intrusted to my hands, but be of good courage, for I will sometime return. In the meantime, my Spirit of the Truth of a universe shall comfort and guide you.

The Purpose of Epochal Revelations ARE.

Authoritative Epochal Revelations

Truth is always a revelation: autorevelation when it emerges as a result of the work of the indwelling Adjuster; epochal revelation when it is presented by the function of some other celestial agency, group, or personality.

In the last analysis, religion is to be judged by its fruits, according to the manner and the extent to which it exhibits its own inherent and divine excellence.

Truth may be but relatively inspired, even though revelation is invariably a spiritual phenomenon. While statements with reference to cosmology are never inspired, such revelations are of immense value in that they at least transiently clarify knowledge by:

1. The reduction of confusion by the authoritative elimination of error.

2. The co-ordination of known or about-to-be-known facts and observations.

3. The restoration of important bits of lost knowledge concerning epochal transactions in the distant past.

4. The supplying of information which will fill in vital missing gaps in otherwise earned knowledge.

5. Presenting cosmic data in such a manner as to illuminate the spiritual teachings contained in the accompanying revelation.