(Matthew 21:12; Mark 11:15; John 2:15) According to (Exodus 30:13-15) every Israelite who had reached or passed the age of twenty must pay into the sacred treasury, whenever the nation was numbered, a half-shekel as an offering to Jehovah. The money-changers whom Christ, for their impiety, avarice and fraudulent dealing, expelled from the temple were the dealers who supplied half-shekels, for such a premium as they might be able to exact, to the Jews from all parts of the world who assembled at Jerusalem during the great festivals, and were required to pay their tribute or ransom money in the Hebrew coin.
Money Changers
Jesus walked into the temple and found it busy with selling and trading. In Matthew, Mark and John he drives out those who bought and sold, and overturns the tables of the moneychangers, along with the seats of those selling doves. John adds that he made a whip of small cords first. People who came to worship had to pass through a marketplace to do it, and Jesus treats that as a wrong done to the house of prayer. Mark 11 is a good place to see what he says about it next.
3 verses
Matthew
Matthew 21:12
And Jesus went into the temple of God, and cast out all them that sold and bought in the temple, and overthrew the tables of the moneychangers, and the seats of them that sold doves,
Mark
Mark 11:15
And they come to Jerusalem: and Jesus went into the temple, and began to cast out them that sold and bought in the temple, and overthrew the tables of the moneychangers, and the seats of them that sold doves;
John
John 2:15
And when he had made a scourge of small cords, he drove them all out of the temple, and the sheep, and the oxen; and poured out the changers' money, and overthrew the tables;
From Smith's Bible Dictionary
William Smith, 1884