Mark 11: 15-17
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; And would not suffer that any man should carry any vessel through the temple. And he taught, saying unto them, Is it not written, My house shall be called of all nations the house of prayer? but ye have made it a den of thieves.
A DEN is a place where people meet in secret, typically to engage in an illicit/criminal activity, in other words, when we do not pray: the church and or our lives become a home for spiritual criminals, it becomes a place of safety, comfort and a place of strategic planning for the devil.
Many brethren are currently under siege as a result of prayerlessness: their businesses, relationships, homes, possessions, etc. Have become a DEN for thieves (Some are courting/dating the thief, some are in business partnership with the thief).
A DEN also suggests darkness, a place that has no light: which talks of ignorance of divine things (no access to revelation) and confusion.
My brother and my sister, may my God stir your spirit so as to cause a spiritual revival in your life and a restoration of your prayer life.
Be Blessed.