This story in the Bible is often misunderstood. We see Jesus being violent and beating the money changers and traders out of the temple. His reasons may be obvious by what He said in the passage quoted above; but there is more to it than that.
In those days the people had to offer a sacrifice to God in the form of an unblemished perfect animal. It could be a pair of doves, a lamb, goat or whatever you can afford depending on your wealth and the gravity of your sin. The people gave the animals to the priests who had them slaughtered and made into a burnt offering.
One reason for Christ's behaviour, apart from the quotation above, is that at the time the people brought their own offerings to the priests and the priests had to decide whether the animal was without blemish and perfect. If the priests decided against that animal then the people had to go an buy another (more expensive) one from the traders in the temple. Hence the collusion between the priests and the traders cheating the poor people out of their money by forcing them to buy a more expensive animal from the traders.
Jesus was angry because instead of the temple being a place of prayers, the priests and traders had made it into an opportunity to cheat and steal from the poor.
