A good book on Greek religion is Gilbert Murray's, The Five Stages of Greek Religion;
https://www.gutenberg.org/files/30250/30250-h/30250-h.htm
I does far more to explain Christianity, than the Old Testament;
"PREFACE TO THE THIRD EDITION
Anyone who has been in Greece at Easter time, especially among the more remote peasants, must have been struck by the emotion of suspense and excitement with which they wait for the announcement "Christos anestê," "Christ is risen!" and the response "Alêthôs anestê," "He has really risen!" I have referred elsewhere to Mr. Lawson's old peasant woman, who explained her anxiety: "If Christ does not rise tomorrow we shall have no harvest this year" (Modern Greek Folklore, p. 573). We are evidently in the presence of an emotion and a fear which, beneath its Christian colouring and, so to speak, transfiguration, is in its essence, like most of man's deepest emotions, a relic from a very remote pre-Christian past. Every spring was to primitive man a time of terrible anxiety. His store of food was near its end. Would the dead world revive, or would it not? The Old Year was dead; would the New Year, the Young King, born afresh of Sky and Earth, come in the Old King's place and bring with him the new growth and the hope of life?
I hardly realized, when writing the earlier editions of this book, how central, how omnipresent, this complex of ideas was in ancient Greek religion. Attis, Adonis, Osiris, Dionysus, and the rest of the "Year Gods" were not eccentric divagations in a religion whose proper worship was given to the immortal Olympians; they are different names given [vi]in different circumstances to this one being who dies and is born again each year, dies old and polluted with past deaths and sins, and is reborn young and purified. I have tried to trace this line of tradition in an article for the Journal of Hellenic Studies for June 1951, and to show, incidentally, how many of the elements in the Christian tradition it has provided, especially those elements which are utterly alien from Hebrew monotheism and must, indeed, have shocked every orthodox Jew."
The origins of the Trinity, which the Catholic Church, the "Immortal Institution," had to erase, leaving the Holy Ghost hovering like an eternal question mark.
