Well, your dream fits very nicely into theory of bicameral mind (you can google it). In short, it says that few thousands center human mind was strongly divided between right and left hemispheres. Right (if more presise - an area of right hemisphere which is now dormant) was one who run the show at those days and it ruled by human showing him (to the left hemisphere) visions of gods and speaking with gods' voices. Due to big social changes bicameral mind collapse and left hemisphere captured control by developing what we call now "consciousness".
So, if this theory is true then this guy is messenger from your "second" (right-hemisphere) mind. It also make sense why he said you what you need to do because it was duty of this brain center to guide one along his life. Looks like in dreams this brain center is still influential and able to communicate. Though to disguise oneself as "god" is somewhat old-fashioned, he should said he is your subconsciousness

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