Jer 2:11-13
"Has a nation changed its gods, even though they are no gods? But my people have changed their glory for that which does not profit. Be appalled, O heavens, at this; be shocked, be utterly desolate, declares the LORD, for my people have committed two evils: they have forsaken me, the fountain of living waters, and hewed out cisterns for themselves, broken cisterns that can hold no water. "

Jeremiah tells us what apostasy is in the above. He tells us that apostasy is replacing the message of God’s Grace ("living waters") with a message of human works ("broken cisterns" that they have "hewed out themselves"). In the case of many churches, it is transfering the focus from Christ to man.

Grace is not common.