WHAT DOES IT MEEEAN?

"I’m in a weird position, because I like rainbows, but I’m not gay. So whenever I go out wearing a rainbow shirt, I have to put “Not gay.” But I’m not against gays, so under that I’ll have to put “… but supportive.” It’s weird how one group of people took refracted light. That’s very greedy, gays."

--Dmitri Martin (comedian)

What does it mean when a "prophet" makes a prophecy which does not come true? What does it mean if they prophesy about something which is guaranteed to happen at some point? What does it mean if their prophecy displays a fundamental misunderstanding of scientific principles, thereby rendering it either mundane or physically impossible? What does it mean if the scientific principles were/are unknown at the time of the prophecy?

Recently I came across a fascinating prophecy from Joseph Smith as I perused Richard Packham's site. Towards the end of his "career" Smith claimed that the Second Coming of Jesus Christ will not come in a year when we can see rainbows. Think about that for a second. He may as well have said Christ won't come so long as pigs don't fly:

“I have asked of the Lord concerning His coming; and while asking the Lord, He gave a sign and said, "In the days of Noah I set a bow in the heavens as a sign and token that in any year that the bow should be seen the Lord would not come; but there should be seed time and harvest during that year; but whenever you see the bow withdrawn, it shall be a token that there shall be famine, pestilence, and great distress among the nations, and that the coming of the Messiah is not far distant.” [emphasis added]

("Teachings of the Prophet Joseph Smith. Joseph F. Smith, 1976., pp. 340-41", and "HC 6:249-254")

I'm sure that anyone with even a cursory understanding of optics can tell you that rainbows, at least in nature, come as light passes through drops of water, which acts as a prism to split the light into all the colors of the rainbow. It is a scientific principle. It works every time, and, best of all, we know why and how it works!

Smith's worldview was such that he believed that rainbows did not exist until after the Great Flood. Seriously. Which would be fine if he had lived before Sir Isaac Newton had explained how rainbows came about through natural processes, but Smith lived much later than Newton, so he either was ignorant of Newton's theory or, well... I guess that would have to be it, huh? 

Some Mormons have convinced themselves that Joseph Smith is speaking allegorically, and that a lack of a rainbow means that no spiritual "light" is coming into the world. Of course, this would mean that even the members of the Mormon Church and its leaders (aka "prophets") would be devoid of such light; but I doubt they have considered that. 

Some other Mormons (same source) have opined that the prophecy is indicative of a severe drought where the utter lack of water would make rainbows impossible. But, again, they fail to think it through as such a drought would be so severe as to make life--especially human life--impossible. Furthermore, the drought would have to last for an entire year before Christ would come to save mankind. If this were really the case then Jesus would be a dick. But let's not forget that Mormons believe that Jesus was the god of the Old Testament (under the direction of god the Father) and called for the Great Flood which killed everyone on Earth except for 8 people and created rainbows to show that he would never do that again; so it seems that they are "OK" with that sentiment...

The Mormon Church appears to be a non-prophet organization...

BONUS MATERIAL:

And now, a double rainbow (What does it meeean?):