Twelve chapters (4-15) of the book of Exodus center around those words, spoken by Moses on behalf of God to the pharaoh (or king) of Egypt, who has enslaved the descendants of Joseph. Ten plagues strike Egypt before the pharaoh obeys. The first is recorded in chapter 7.
In the sight of Pharaoh and of his servants, Moses lifted up his staff and struck the water in the Nile, and all the water in the Nile turned into blood. The fish died, and the Nile stank, and... there was blood throughout the land of Egypt.Then things take an unexpected turn.
But the magicians of Egypt did the same by their secret arts.What was the point of that?, I want to ask. (The standard conundrum, where did they get the water?, doesn't seem to bother the biblical author a bit.)
The magicians don't have a helpful solution to offer (like changing blood back to water, for instance). All that they can achieve is to undermine the story Moses is telling, the story which relates this mysterious disaster to their country's slave labor policies - to the source of their wealth.
Their counternarrative doesn't last long - they fade out of the story a couple of plagues later - but while it does, it serves to give Pharaoh some cover for his business-as-usual approach:
So Pharaoh's heart remained hardened... Pharaoh turned and went into his house, and he did not take even this to heart.
According to a midrash quoted by Brevard Childs in his commentary, Pharaoh believes that he can afford to be unconcerned; his wealth will shelter him from the troubles that his people must suffer. "You don't trouble me", this story has him replying to Moses, "for, if I can't have water, I'll drink wine."
Any excuse for inaction.
Photo entitled "Vampire Spa" by Flickr user jcoterhals, licensed under Creative Commons.