In this story, on the Monday after Palm Sunday, Jesus re-enters Jerusalem, goes to the temple, and drives out the moneychangers and people who were selling animals for sacrifices. He overturns tables, and takes a whip, and uses it to clean out the temple.
It's a powerful story, and one that shows a different view of Jesus's personality than the healer or preacher that is so often described. Plus, it doesn't seem all that unreasonable for there to be moneychangers in the temple - a little like the bureaux de change at airports. Too, it seems convenient to have people there selling animals to those who need them for the prescribed sacrificial offerings.
So, what's the story about?
The moneychangers and sellers of animals represent evil loves in our lives that cloak themselves in external piety. They have to be driven out, unmasked, and scourged.