It's a hebrew letter which looks a lot like an apostrophe. Why is it important? It reminds me that we need to take the scripture seriously. Especially in it's original hebrew/greek/aramaic as it was originally written. That's the reason I first started to learn hebrew.
Because Jesus did.
Jesus himself said 'Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfill. For verily I say unto you, 'til heaven and earth pass, on jot [yod] or one tittle shall in no wise pass from the law 'til all be fulfilled.' Matt 5:17-18
As if that wasn't enough, he also gives us an example of how to read and interpret scripture in the most literal way, using a quote from psalms to confound the pharisees - the learned teachers of the scriptures. Matt 22:41-15
Jesus calls the pharisees together saying 'who do you think the Christ is?' and they answer 'the son of David'.
So Jesus quotes back to them psalm 110 saying 'The Lord said unto my Lord, sit thou at my right hand, until I make thine enemies thy footstool. If David calls him Lord, how then is he his son?'
What you miss in english is the differences in the word for Lord used here. The first Lord is written 'YHWH' or Yahweh and is the standard name used for God in the old testament. The second word is 'Adonai' with a yod at the end. It looks like this:
That yod changes the meaning into a possessive. The text doesn't simply say, 'God said to THE Lord...' It says 'God said to MY Lord. This couldn't be a natural child of David's that was being prophesied, because David was saying that even he would call Him Lord.
I love the way this passage finished too, 'And no man was able to answer him a word, neither darest they to ask him any more questions from that day forth.'
If Jesus, who was Himself God, accepts that scripture is accurate to the point that even the punctuation is enough to build a theological argument from, the surely it is accurate enough for us to take it very seriously?
So don't let a culture, even inside your churches, rob you of the precious revelations that scripture can hold for you, by telling you that it contains human error, or that it's only allegorical. If it was good enough for the Messiah to believe it inerrant, it should be good enough for you too.