The temple in Jerusalem, which was consecrated to the Lord, had attracted all sorts of businesses who traded profitably rather like the shrine shops in pagan temples.  In some ways it seemed legitimate and practical: worshippers travelling a long way would prefer to buy an animal or bird for sacrifice in Jerusalem rather than carry or drive it from their home village.  But, when they arrived at the outer court of the temple (the Court of the Gentiles), where these animals were being traded, no coin with an image of a foreign ruler or pagan god on it would be accepted, only Jewish Temple Mon

In the week before Jesus was crucified, even though He knew exactly what would happen (Luke 9:22) He was not afraid of those plotting to kill Him.  He chose to teach publicly in the temple (Luke 20:1) so that the disciples could later understand how to teach essential doctrines to the Early Church (John 12:16).  This parable was a prophetic description of the hatred of the religious establishment against Him.  The priests and religious lawyers who were hovering in the back of the crowd knew that the story described them, and it intensified their lethal hatred (Luke 20:19).  

Jesus was telling a story about rebellious tenant farmers who had no respect for the owner of the vineyard or his representatives or his son (Luke 20:9-19).  Indeed, they decided to kill the son, assuming that they would then inherit the property as sitting tenants.  So Jesus challenged His listeners to decide what would be the right action for the vineyard owner to take.  Clearly, those who had been left in charge of the farm had demonstrated their untrustworthiness.  The only sensible conclusion would be for the owner to dismiss the farm managers and employ others who could be trusted.

Within days of Jesus' appointment with death, His accusers still had no way to bring Him to a legal trial.  Although they had decided that He must die, under Roman occupation, they had no authority to execute Him: and He never did anything to offend the authorities.  So, the Jewish lawyers hoped that He could be provoked into incriminating Himself in some way, perhaps by speaking against Caesar - which would be treason, a capital offence (John 19:12-16).