There is no denying that Jesus, as we know him, does bare some resemblances to a handful of other gods, not only Greek in origin, but from all over the Mesopotamian region. Gods such as Dionysus, Hercules, Perseus, etc, were born of a virgin. God such as Attis, Tammuz, Osiris, El, etc, died, and then rose again (either in a literal or symbolic sense).
The argument from a comparative religion standpoint does not specifically say that early Christian “stole” ideas from other religions that they thought sounded cool, though it is often misinterpreted as such. It is instead a discipline of stepping back and looking at different religious ideas to see what they have in common. What sorts of themes and concepts do people revere? What makes people/objects holy or sacred? The study of comparative religion is more concerned with what goes on in the human mind than what goes on in any unseen world out there.
The Evolution of Jesus
The image of Jesus, as far as we can tell from the records that we have, did not appear out of whole cloth. Instead, the Jesus story appears to have grown in the telling. The earliest dated documents (the epistles, the Didiche, etc) talk of Jesus the Christ (the Greek reading of Joshua the Anointed) only in terms of a heavenly savior, an intermediary son through which his flock can get to know God the Father. The references by Paul that Jesus was revealed to him through the scriptures leads us to believe that he came to know of Jesus through a discipline know as pesher, pesher being a method of finding hidden messages or prophecies by re-interpreting already existing religious writings, like the Torah. A practice like this may sound strange, but you are probably more familiar with it than you think, since it is still practiced today. Any time someone claims that God is giving them a personal message through some arcane interpretation of an ancient Bible verse, they are practicing pesher (though probably not in the same sophisticated way that the New Testament authors practiced it).
The next stage of development was the writing of the first gospel: The Gospel According to Mark. This document, originally untitled, is by far my favorite gospel preciously because of the heavily mythological feel it has. It reminds me very much of the Greek hero stories. It tells the story of Jesus walking around on Earth, something that had not been done yet, in a third person method (no claims of eye witness). Jesus is shown having the Holy Spirit enter into his body (apparently giving him his supernatural essence), he heals a deaf/mute by sticking his fingers in his ears and spitting, controls the weather, feeds a bunch of people with a food miracle, foretells the end of the world, then is killed, the holy spirit leaving him. There is no virgin birth in gMark. There is also no earthly resurrection of Jesus after his death; once the women go to the tomb, they find it empty and flee, telling no one. Jesus had, apparently, been pulled up directly to heaven. (the oldest copies of gMark end at chapter 16 verse 8, and the newer copies we have that continue past that point bear show a different writing style, leading experts to believe the narrative was appended at a later date to keep up with the evolving story).
The gospel of Mark is written using two distinctive methods very popular at the time: midrash and the emulation of Homer. Midrash is a method of re-writing ancient scriptures as a means of conveying lessons to a modern audience. The reason the Homeric epics the Illiad and the Odyssey were emulated was because, in the Hellenistic world, they were used as a method to teach students to read and write. Anyone educated in Greek, the language the gospels were written in, would copy the stories, then re-write them in prose form, or write other stories using the outlines laid out by Homer.
Other literary markers in mark include it’s two part outline: Mark is divided into two section, Jesus’ ministry in Galilee, and his time in Jerusalem. Each section features 5 miracles that mirror each other, a feature that is obviously pure narrative, and not a relation of actual historical events.
The next major stage in the evolution of the Jesus story was the composition of the Gospel of Mathew. Written probably 20 years after Mark, it used the initial story Mark had written(even using direct quotes from it), adding to it a list of sayings that had been associated with Jesus, commonly refereed to as Q, and breaking the structure out into 5 sections in emulation of the Hebrew Pentateuch instead of Homer. The book then uses Moses as a model, having Jesus preach on a mount, adding a massacre of the innocents, and a flight into Egypt. Taken as a whole, the book is a classic midrash, re-telling the law code of Moses to the day’s Hellenistic Jews.
Mathew also adds to the story an earthly resurrection and a virgin birth, much like a Greek hero.
Possibly as late as the middle of the second century CE, the gospel story was re-written once more, this time in the writings known as the Gospel According to Luke and the Acts of the Apostles (which really focuses on Paul). Luke appears to be the first of these gospels that really believes all the events told of in the previous documents really occurs and is attempting to write them as history.It appears to have been written for a Roman audience, since the Roman authorities in the story are relieved of responsibility for Jesus’ death. The author, again his true identity unknown to us, also relied heavily on the histories of Josephus and other sources to create what he believed would have been the history surrounding the early church.
So, is Jesus based on the Greek gods? Well, there may be some of that in there, but it would hardly be an intentional addition. Most elements of the story would have been added as the story grew.
The heavenly Jesus is a phenomena of the ancient world that we are well aware of: the intermediary son. It happened in many cultures when the concept of god evolves into that of an esoteric and philosophical being that many of the common people no longer felt they could relate to anymore. The intermediary son gives a personality to the god head.
The second stage, the earthly Jesus appears to have started as a narrative method of relating the story to new converts. When writing the story, the most popular aspects of hero would very naturally have been appealed to.
The third stage, adding historicity, would be done once the story gains importance.
At each stages more attributes would be added to the Jesus story, some of them Greek, some Hebrew. The Hebrew concept of a messiah restoring the Hebrew rule to Jerusalem became an intermediary son, a concept that was indeed very popular in the Mystery Religions.