If following Jesus should be marked by uncontainable joy, it should also be marked by zeal for worship and passion for social justice. The timing of this event adds another interesting element. The story of the cleansing of the temple appears in the Synoptics at the end of Jesus ministry when he entered Jerusalem for the last time. But John places the event three years earlier at the beginning of his public ministry. I think both could be true.
Sin has a way of coming back.
There is a persistence about evil. This duck walked into a restaurant one day and asked the man if he had any duck food. The waiter looked down at the duck and told him to get out of there, he didn't have any duck food and this restaurant was no place for ducks anyway. The next day the duck came back and asked again if he had any duck food. I don't carry duck food and this is no place for ducks.