“It is written, ‘And My House shall be a house of prayer' ...” (Luke 19:46)

“It is written, ‘And My House shall be a house of prayer’; instead you have made it 'a den of thieves!’” (Luke 19:46)
Jesus has entered into the Temple in Jerusalem and he is railing against those who are offending God by doing business within the grounds of the Temple. Here is the verse before this one:
As Jesus entered the Temple grounds, he began driving out those who were selling. (Luke 19:45)
The Book of Matthew indicates Jesus was even more adamant:
Jesus entered the temple courts and drove out all who were buying and selling there. He overturned the tables of the money changers and the benches of those selling doves. (Matthew 21:12)

Why did Jesus turn over the tables?

Jesus has walked into the courtyard of the temple of Jerusalem and he is turning over tables. This is no trivial thing. Jesus is very upset. Why?

Because he understood that the Temple was the place where God is to be worshiped. And those merchants are using these grounds to make money. They are essentially desecrating the House of God and thus interfering with the purpose of the Temple - to offer a respite from the material world and give those who are devoted a place to reconnect with God.

This is confirmed by the fact that the statement above by Jesus is actually quoting two passages from two different scriptures at the same time:

In the first part of Jesus' statement, Jesus quotes Isaiah:
“And foreigners who bind themselves to the LORD to minister to Him, to love the Name of the LORD, and to be His servants, all who keep the Sabbath without desecrating it and who hold fast to My covenant—these I will bring to my holy mountain and give them joy in My house of prayer. Their burnt offerings and sacrifices will be accepted on My altar; for My house will be called a house of prayer for all nations.” (Isaiah 56:6-7)
In the second part of Jesus' statement, he is quoting the Book of Jeremiah:
Has this house, which bears my Name, become a den of robbers to you? (Jeremiah 7:11)
So why is the House of God so special? This is the place where the Supreme Being is supposed to be worshiped, and praised. Thus, it is the place where God can be approached - and people can come in and pray and make offerings to God:
Then Jesus looked up and saw some wealthy people putting offerings into the Temple chests. He then saw a poor widow offered two small copper coins. (Luke 21:1-4)
We find many other instances where Jesus also encouraged people to make offerings to God at the Altar of the Temple:
“Therefore, if you are offering your gift at the altar and there remember that your brother or sister has something against you, leave your gift there in front of the altar. First go and be reconciled to them; then come and offer your gift." (Matt. 5:24)
"You blind men! Which is greater: the gift, or the altar that makes the gift sacred?" (Matthew 23:19)
So we find that indeed, Jesus supported making offerings at the Altar of God at the Temple. And he considered the Altar to be sacred. Here we find the central issue that caused his anger at the merchants in the Temple:

They were utilizing what was supposed to be a place to worship and offer to God for their own purposes.

This is offensive, not only to Jesus, but to the Supreme Being. This is why Jesus was so upset. Because they were offending Jesus' beloved - the Supreme Being.

Can a church or temple not be used for commercial purposes?

This use of God's house as a place where people exercise their quest to make money was not isolated to the Jewish Temple in Jerusalem. Today we find this is also going on in so many institutions today.

We find so many churches and temples being used for rummage sales, or flea markets, bake sales, Easter egg hunts and so many other materialistic activities. Just as the Temple market upset Jesus, these activities are also offensive to Jesus and the Supreme Being when they are being held on the grounds of today's churches and temples.

But they might say, 'the money is going to pay the pastor's salary,' or 'the money is going to pay for this or that church business.'

How is this different than the merchants at the Temple? They were also being paid so they could take the money home - just as the pastor is getting paid so he could buy a new car or a nice house. In reality, so many of these churches and their institutions have basically become businesses. They are paying salaries to their pastors and so many others no different than a business does.

In this way, the pastors have become businesspeople. They have completed their seminary degree and come to work for some institution just as a business graduate will come work for a corporation. What is the difference? They are both being paid for their services. They are both collecting a salary. And both entities (church/business) are going out to bring in customers (parishioners) so that they can pay for the church institution operations and pay the pastor's salary.

They have effectively turned what was supposed to be a place of voluntary offering, service and worship into a place of business.

Should priests and pastors be paid salaries?

Aren't the pastors and priests supposed to be paid? How would they survive otherwise? And aren't they being paid from the donations of the parishioners?

It would certainly be fine if the parishioners were specifically giving a donation directly to the priest or pastor. There is nothing wrong with such teachers receiving donations. And there is nothing wrong with a teacher being supported by his or her followers.

The problem comes with the salary. And the organizational arrangements that have to do with money. The typical setup of these sectarian institutions is they make a contract with the pastor or priest. They sign a contract as a salaried employee of the institution or church. Just as a businessman would sign a contract with a business for a salaried position.

This means that the priest or pastor is not donating his time. There is no voluntary service. The time he spends as a pastor or priest is being compensated with money. It is a professional arrangement.

This means that the preacher now has to please their employer. They must preach what the institution wants them to preach. They are now obliged to the institution - and those who manage that institution. For example, if the church deacons make the decisions on who the church hires - then the preacher must please the deacons. He is no longer allegiant to the Supreme Being or Jesus. He has sold himself out in exchange for a salary.

This runs contrary to the very basis for devotional service. It runs contrary to the basis of making offerings to God. The priest or pastor should be teaching by their example. They should be offering their time voluntarily - as a service to God. They should be preaching without being compensated for their time.

Surely, if the followers of the priest or pastor did make donations to him, those donations could be used by the priest for the purpose of survival. There is nothing wrong with that. But as soon as a second party or organization steps in and there is an arrangement made as a salary in exchange for the services, it becomes a business. It becomes a professional career to the priest or pastor.

Once this takes place, there is no offering. They already have their reward. They are being compensated for their service. It, therefore, cannot be loving service.

Why was Jesus preaching about loving service to God?

“My food,” said Jesus, “is to do the will of Him who sent me and to finish His work." (John 4:34)
Jesus didn't make any money from his preaching. And neither did his disciples. In fact, Jesus specifically instructed his disciples not to even carry a bag as they preached:
“Take nothing for the journey—no staff, no bag, no bread, no money, no extra shirt." (Luke 9:3)
Why? Why couldn't they pack a bag?

Because Jesus didn't want them collecting things or money in return for their preaching. He wanted them to receive nothing material in return for passing on his teachings.

He didn't want them to become professional preachers.

This was contrary to the priests of the Jewish temples - whom Jesus railed against:
“Beware of the scribes – who like walking around in long robes receiving respect in the marketplaces. And have the important seats in the synagogues and the places of honor at the feasts – yet they forcibly appropriate widows’ households and for appearances’ sake offer lengthy prayers. They will receive the greatest consequences.” (Mark 12:40)
When the man of the house passed away, these Jewish organizations would appropriate the household wealth for the temple treasury. Why? Because they received salaries. They were businessmen and their business was to profit from the temple. Their goal was to live luxuriously at the cost of their supposed followers.

While today's sectarian institutions don't seem to forcibly take from widows' households, some do something that is practically as bad. They trick people into donating to their organizations. For example, some evangelical preachers will promise to pray for anyone who sends in a donation. Such trickery in the name of Jesus and the Supreme Being is the gravest of offenses: Using preaching - whether within a church or on television - to profit from those who are seeking salvation.

This includes those who make other promises, including the promise of healing people's physical bodies. Jesus was clear that these people were not to be accepted as his followers:
"Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven. Many will say to me on that day, 'Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?' Then I will tell them plainly, 'I never knew you. Away from me, you evildoers!'" (Matt. 7:21-23)