From Rod Rosenbladt’s chapter “Christ Died for the Sins of Christians, Too” in Christ the Lord: The Reformation and Lordship Salvation:
I hear the reader asking, “Well then, is saving faith just a matter of knowing facts?” Hardly, and the Reformers knew that. They distinguished between historical faith and saving faith.
Historical faith has human speculations as its goal or end. It is an intellectual acceptance of facts concerning Jesus’ life, work, and death; nevertheless, it comes only from the human mind, acknowledging the facts, but remaining basically uninvolved with the One that caused the facts to happen. And the key phrase that Luther used was that the person who just has historical faith believes that none of this is pro me, or for me.
Once a person comes to accept that this whole action summed up in the Nicene Creed is for me, then, said Luther, we are talking about the kind of faith that saves. There we have an active embracing of the Son of God and his self-sacrifice.