Riddle Me This

Riddle me this and riddle me that.
It is the power of God unto salvation.
 Yet harmless as a lamb without a willing participant.

As ferocious as a wounded dog for anyone who stands on its principles. 

And gentle as a lamb for anyone who is sheppard by it.
Hint

It is better to fall on the rock than for the rock to fall on you.

Gairey