|Left: the souls of Ra and Osiris squaring up with each other, symbolic of being equal in supreme god power, in the form of Osiris-Ra or Ra-Osiris. Center: a depiction, from the Papyrus of Ani (1250BC) of Ra in the form of an ankh, being born out of the djed pillar (backbone) of Osiris. Right: an image (c.1150BC) Ra in the form of the sun being born out of the evergreen tree (see: Christmas tree) form of Osiris.|
In the Jewish recension (c.900-200 BCM), Osiris-Ra supreme god motif, promoted in Thebes, was recast into the Moses-Abraham motif, admixtured with Atenism ideas, supposedly, by a sect of reformed Egyptian priests called by Herodotus the Cohens, who therein made the Old Testament of the Bible via a god to prophet rescript technique, wherein Osiris became Moses and Ra became Abraham, thereby doing away with the previous god reduction techniques of god synretism (e.g. Amen-Ra) or god incarnation (e.g. Amen).
The following are related quotes:
“Amongst modern scholars, Lepsius, in identifying Osiris with the sun, appears to rely mainly on the passage of Diodorus already quoted. But the monuments, he adds, also show “that down to a late time Osiris was sometimes conceived as Ra. In this quality he is named Osiris-Ra even in the Book of the Dead, and Isis is often called ‘the royal consort of Ra’.” That Ra was both the physical sun and the sun-god is undisputed; but with every deference for the authority of so great a scholar as Lepsius, it may be doubted whether the identification of Osiris with Ra can be accepted as proof that Osiris was originally the sun.”— James Frazer (1907), Adonis, Attis, Osiris 
“The very sub-title of the Book of the Dead: the Chapters of Going Forth by Day, evokes an image of the soul emerging into the restorative rays of the sun’s light after revival during the nighttime in the underworld. Most Egyptian mortuary texts are like the Book of the Dead in this respect—they view the life beyond the grave as combining a chthonic Osirian afterlife with a solar or stellar afterlife. The Egyptian sense of balance meant that both aspects of life beyond the grave were necessary for the survival of the dead. The chief celestial deity, the sun god Ra, was therefor a major figure in the Egyptian concepts of the afterlife, second only to Osiris.”— Ogden Goelet (1994), “A Commentary on the Corpus of Literature and Tradition which Constitutes the Egyptian Book of the Dead (the Book of Going Forth By Day)” in The Egyptian Book of Dead (pg. 149); in Revised and Illustrated Edition (2015) (pg. 159) 
“In the religious texts that adorned the Theban royal tombs of the New Kingdom, a new, important god of the afterlife makes his first appearance: Osiris-Re.”— Ogden Goelet (1994), “A Commentary on the Corpus of Literature and Tradition which Constitutes the Egyptian Book of the Dead (the Book of Going Forth By Day)” in The Egyptian Book of Dead (pg. 149); in Revised and Illustrated Edition (2015) (pg. 160) 
1. Budge, Wallis. (1904). The Gods of the Egyptians, Volume Two (pgs. 148, 334). Dover, 1969.
2. Frazer, James. (1907). Adonis, Attis, Osiris (pg. 352). MacMillan.
3. Faulkner, Raymond. (1972). The Egyptian Book of the Dead: the Book of Coming Forth by Day: Complete Papyrus of Ani, Featuring Integrated Text and Full-Color Images (translator: Ogden Goelet; Preface: Carol Andrews; Introduction: Daniel Gunther; Foreword: James Wasserman) (Amz) (pg. 156). Chronicle Books, 2015.