Why are there different versions of the First Vision?

Joseph Smith recorded at least three different versions of the First Vision and that they differ substantially.  The modern LDS Church does utilize the 1838 account of the "First Vision" as a central point in both its proselyting effort as well as in its theological teachings regarding the nature of God. Smith also gave accounts in 1832 and 1835.

It is important to point out, however, that Joseph Smith never placed much emphasis on the First Vision and did not utilize it in his teaching or as proof of his theology.  It wasn't until much later that the Church (after Smith's death) began to utilize the First Vision in this way. 

Theophonies were somewhat common in New England during this time period and many others, in addition to Joseph Smith claimed to have had visions of God and Jesus, or Jesus alone, or angels alone.

Why do the versions vary?  Why did it take so long for Joseph Smith to publicly tell his story of the First Vision?  Scholars differ in their views.  However, contemporary accounts of Joseph's family and peers seem support the idea that young Joseph did indeed tell his a vision during his teenage years and that he did receive negative feedback and treatment from at least one member of the clergy.

Church critics often like to cast doubt on whether or not religious revival was present in Palmyra during 1820. This assertion is problematic for at least two reasons.  First, there is no scholarly consensus on this issue and second, this entire area of New England was called the "burned-over district" because it was known for its evangelical preaching, circuit ministers, and overall religious zeal.  There may not be any direct evidence for a *specific* revival in 1820 ;  However, the entire area was engulfed in this evangelical furor which took hold of this region for a period of several years.  Thus, it is quite likely that young Joseph -- whether he was 14, 15, 16, or 17 was at some point caught in this atmosphere of religious zeal and felt its impact.  Indeed, there is no question that religious conflict or rather, strong disagreement -- was present in the Smith home.

D. Micheal Quinn has written an excellent article on the subject of Palymra revivals.