According to Bruce R. McConkie, a cherub is an angel of some particular order or rank to whom specific duties and work are assigned. That portion of the Lord's word which is now available among men does not set forth clearly either the identity or work of these heavenly beings. The concept of sectarian scholars that they are "mythological creatures," who filled for the Hebrew people the same position that the griffins did for the Hittites, is utterly false. (Griffins were supposed to be winged sphinxes having the bodies of lions and the heads and wings of eagles, and they were in fact mythological creatures.) [Bruce R. McConkie, Mormon Doctrine, p. 124]
“God Placed Cherubim and a Flaming Sword”
In Alma 12:21, Antionah, who was a chief ruler among the people of Ammonihah, asked an intriguing question:
What does the scripture mean, which saith that God placed cherubim and a flaming sword on the east of the garden of Eden, lest our first parents should enter and partake of the fruit of the tree of life, and live forever? And thus we see that there was no possible chance that they should live forever.
According to McConkie and Millet, Antionah's query is actually a valid one: If, according to the earliest scriptural accounts [and according to the chief ruler's way of thinking] God prevented Adam and Eve in Eden from partaking of the fruit of the tree of life (and thereby prevented them from living . . . forever), why would Alma and Amulek speak of the gospel plan as a means whereby men and women could live forever through Christ? Alma of course, will explain that God . . . made known a plan whereby [his children] could be made ready, after a life of mortality, to enter through Christ [or through His covenant actions and our covenants built upon His covenant actions] into resurrected immortality. . . . If Adam and Eve had been permitted to partake of the fruit of the tree of life before living out their mortal lives, they would have been taken into immortality without the experience--the pains, the struggles, the opportunities to overcome, the posterity, and thus the joys---of this life. They would have been damned in their progress. And the rest of us would have known no progress; we would have remained forever as unembodied spirits. [Joseph Fielding McConkie and Robert L. Millet, Doctrinal Commentary on the Book of Mormon, Vol. III, pp. 88-89]