Years ago, coal miners took a caged canary down into the mine with them, because canaries are extremely sensitive to carbon monoxide and methane. The earliest mines didn't have ventilation systems, so canaries helped detect toxic gases long before humans could.
The canaries served as a warning system, an audible and a visual cue as to the condition of the air the miners were breathing. As long as the miners could see that the canary was alive, and could hear the canary singing, the miners knew that the air was safe to breathe.
A silent, dead canary meant that the miners needed to evacuate immediately—their environment had turned toxic.
The phrase "canary in a coal mine" has come to refer to someone or something that provides an early warning of a potential crisis.
Each year PTM/CWR dedicates one week in March as a time when we can all join together, considering the plight of people who are trapped in religious coal mines. They are breathing toxic fumes—and of course anyone who finds themselves in such a place needs help in identifying how toxic their spiritual environment is.
We call it our Day of Prayer for Religious Captives. Ephesians 2:4-5 tells us that the only reason we are spiritually alive is because of the love of God—he has saved us from spiritually unhealthy places by his grace.
Like a spiritual coal miner, we must carefully monitor the degree to which God's grace is being seen and heard in any spiritual environment in which we find ourselves. The degree to which grace is absent, ignored or even maligned and made fun of is the degree to which any religious environment is spiritually unhealthy and toxic.