The Urantia book was authored by demonic influences, not Yahweh

For the time will come when men will not put up with sound doctrine. Instead, to suit their own desires, they will gather around them a great number of teachers to say what their itching ears want to hear. They will turn their ears away from the truth and turn aside to myths. 2 TIMOTHY 4:3-4

For me the Urantia Book's mark of "demonic" influence is its total lack of understanding regarding the Christian doctrine of sin or salvation. Other religions are constantly portrayed as "primitive" religions practiced by "primitive men."

Biblical concepts are exchanged for an evolutionary theory which is used to explain the basis for religious differences. The book quotes and paraphrases several portions of the Bible and distorts key biblical truths. For example:

As the savage mind evolved to that point where it envisaged both good and bad spirits, and when the taboo received the solemn sanction of evolving religion, the stage was all set for the appearance of the new conception of sin. p. 975

The concepts of substitutionary atonement and propitiation with blood are viewed by the Urantia as grotesque and grossly primitive. Primitive man believed that something special must be done to win the favor of the gods; only advanced civilization recognizes a consistently even-tempered and benevolent God. p.974

Similar to other cults, the Urantia book speaks of:

the Fatherhood of God and the universal brotherhood of all men. p. 1085
and

God...who dwells, by his spirit, in every sincere human soul. p. 1453.

The Urantia book is said to be written by many people but due to the extraordinary volume of detailed and complex information, it is difficult to conclude that the Urantia Book was the product of multiple imaginations. While that is not out of the realm of possibility, a more plausible explanation is some form of genuine demonic influence.

Similar to the claim for the Book of Mormon, divine revelation did not cease with the 66 canonical books of the Old and New Testaments. However, the Mormon product pales by comparison to the encyclopedic detail and complexity of the Urantia Book. The fact that the Urantia Book agrees with the Bible in certain areas confirms the fact that the author (human and/or demonic) had some level of understanding regarding spiritual themes.

Further, while select statements found in the Urantia Book are not necessarily contradictory to the Bible, a number of critical topics are diametrically in disagreement with sound, orthodox Christian teaching.

We may resort to pure revelation only when the concept of presentation has had no adequate previous expression by the human mind. p.16

...in making these presentations about God and his universe associates, we have selected as the basis of these papers more than one thousand human concepts representing the highest and most advanced planetary knowledge of spiritual values and universal meanings. Wherein these human concepts, assembled from the God-knowing mortals of the past and the present, are inadequate to portray the truth as we are directed to reveal it, we will unhesitatingly supplement them, for this purpose drawing upon our own superior knowledge of the reality and divinity of the Paradise Deities and their transcendent residential universe. p. 17

The Holy Spirit, via the Apostle Paul, instructs believers that spirit beings were capable of communicating with human beings and warned the Christians living in the providence of Galatia to beware of such apocryphal messages.

But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned [anathema]! Galatians 1:8

The proverbial "nail in the coffin" (for me at least) is found on page 1343. The source of the book clearly states that the majority book was based on already available sources.

In carrying out my commission to restate the teachings and retell the doings of Jesus of Nazareth, I have drawn freely upon all sources of record and planetary information. My ruling motive has been to prepare a record which will not only be enlightening to the generation of men now living, but which may also be helpful to all future generations. From the vast store of information made available to me, I have chosen that which is best suited to the accomplishment of this purpose. As far as possible I have derived my information from purely human sources. p.1343

So that you have it. The author (or authors) of the Urantia book readily admit that it is based on "purely human sources".

[link to en.wikisource.org (secure)]