"Thus says the LORD of hosts, the God of Israel: Amend your ways and your doings, and let me dwell with you in this place. Do not trust in these deceptive words: 'This is the temple of the LORD, the temple of the LORD, the temple of the LORD.'"
"If you build it, he will come," was the famous phrase from the 80's movie FIELD OF DREAMS. It worked for a baseball field in Iowa... but Jeremiah tells us that it won't necessarily work for temples and churches. Oh sure, people may come... in droves! But don't expect God to show up just because it's a "house of worship."
In Jeremiah 7, God has the prophet chastise the people for their actions, not their worship. They'd been acting unjustly - oppressing orphans, widows & foreigners, "shedding innocent blood," swearing falsely, committing adultery, stealing, following other gods, etc. Then they'd waltz into worship and assume that God would be there waiting for them with outstretched arms. WRONG! God called their so-called houses of worship, a "Den of robbers" (a phrase Jesus would use later, when he confronted the temple moneychangers!).
"Don't trust in these deceptive words," Jeremiah is told. "The temple of the LORD..." Hymns, songs, prayers, rituals... no matter what we may say about God in our churches, that's no guarantee God is "on board" with us. We have to walk the talk with our actions. How sad that our failure to live out our faith may have caused God to leave our churches - and we may not have even noticed! Ouch...