Jerusalem in the bible was a place ( temple) where the children of God offers sacrifice to God to forgive them when they sin against God, pray to God to answer their prayers . It was a place that they come to listen to God through the mouth of the priests in our present day you can call say pastors, bishop, evangelist etc
Isaiah 56:7 : Even them will I bring to my holy mountain, and make them joyful in my house of prayer: their burnt offerings and their sacrifices shall be accepted upon mine altar; for mine house shall be called an house of prayer for all people.
From God word the house of prayer where is joy, the bible says in the presence of God is fullness of joy, where burnt offering and sacrifices are offered to you which may be in form offering, tithe and vows in our present day. It a place that the children listens to God's word for encouragement,discipline and upliftment to next level.
Jeremiah 7:11:Is this house, which is called by my name, become a den of robbers in your eyes? Behold, even I have seen it, saith the LORD.
It was revealed to Prophet Jeremiah which he prophesied in the old testament that the house of God has turn to be den of thieves . A place which was meant to be sacred place has turn to be a place of business transactions without no respect and regard to God.
Matthew 21:13 : And said unto them, It is written, My house shall be called the house of prayer; but ye have made it a den of thieves.
Jerusalem a temple that was meant to worship place where the Israelites worship , encourage one another to be strong in faith, listen to God's word has turn to a place of buying and selling, offering business transactions that is not on line with God's word and will.
Why is turn to be den of thieves is that they understand who they are in God , understand that the temple of God is meant to be kept holy at all times. Also due to greed and selfish interest they turn it to be a den of thieves.
As well no knowledge about the word of God because if they do they won't turn the house of prayer a place we seek solution to our problems to another things which is not off God.
Bringing it to our present days, many temples has turn to be den of thieves extorting money unnecessary from the members in the name of offerings and seeds. Recognizing those who has money more than those who don't have.
Not feeding the sheep's (members) with the right word for their spiritual growth, that's why is important as a christain to run away from any form idols in the God's temple because one day we will give account of how we live our lives.
God bless us as we do His will