Poland's bishops marked their country's centenary of independence by warning freedom could be lost again if Poles abandon their Catholic faith.

In a pastoral letter for the November 11 centenary, the bishops said love of homeland was a divine command and was expressed through "daily civic honesty, readiness to serve, and dedication to the common good."

"Our homeland's painful history should sensitize us to threats to the nation's spiritual freedom and sovereignty," the bishops said.

They said independence required not just "armed struggle, and political and diplomatic efforts," but "resolute faith and prayer." They said Poland was being "morally and spiritually weakened" by "a spreading captivity, especially among young Poles, from alcohol, drugs, pornography, internet threats, gambling, etc."