I am still on the trail of distinguishing propter Christum versus propter fidem (see previous post).
I think we may determine where we are standing based on the hypothetical question that God may ask of us. The question is this; how shall we answer God if he asked us - why should I let you come into my heaven?
How we answer this question will say where we are standing. We will set aside the answer "because I was a good boy". We know that won't wash because it would not answer why Jesus was on the cross.
One can answer the question in the following ways, then...:
a.) "because I believe Jesus died on the cross for me"
b.)"because Jesus died on the cross for me".
Notice that the difference is subtle and may seem faint, but again, they are worlds apart, they are as different as night is from day.
With a.) you are still inserting yourself or what is inside you into the equation. Here one is still posing to God what is happening in one's self, and hence, I would say you are doing a propter fidem. To be honest with you, I think this view reduces in effect to the Roman Catholic understanding of justification. I am sorry to say, but you would be practically functioning as an RC in your understanding of the Christian faith.
With b.) we are giving as plain as the answer can be given, there is nothing about you doing or having anything, it is just Jesus doing something for you. Here Jesus comes in between you and God. Sure, you do believe, but you are confessing what you believe, that He did it all for your sins. I would say this is propter Christum, none of you but all of Christ - solus Christus.
I heard Dr. Nagel said one time in a broadcast of Issues Etc, saying that - when you go to the Bible (I think he meant in the Epistles), each time you see "faith" substitute in its place "Christ" and you will understand what being justified through faith means. So for example we can get Romans 5:1 and try it there. Did you see the effect? Nagel's substitution works because Jesus' death, burial and resurrection is for our justification.
If you asked me, I think, Dr. Nagel's advice is pretty good.