When read word for word in the OP there really is no IN and OF Christ mentioned. Paul merely juxtaposes justification by faith as opposed to law announcing it a dead end. The irony is that this so-called justification by faith became law later on. Can't quite catch on to what Justification is supposed to mean in either case. What justifies man if not the fact that he's here. What would justify his disappearance if not another act of god or himself being the cause. For anything to be justified requires an overt reason and not just a single word abstraction which denotes nothing but can connote anything.

I find it not so hard to understand the difference between in and of. There is the faith OF Christ as possessed and revealed by him culminating in his Resurrection and the faith IN Christ which Paul internalized and carried forth as his mission to proclaim the means by which man is justified compared to the external world of Law devoid of any such justification. Note what it states in your quote...even we have believed in Jesus Christ, that we might be justified by the faith of Christ.

Paul couldn't have proceeded without that prior incarnation of faith manifested in Christ.

Since you proclaim it as an essential distinction, you must already have some idea as to what that is and not merely proclaim as some mystery one must ponder. Actually the biblical quote is quite clear in its meaning. If there is a mystery, it is the mystery of faith itself.

Faith is the belief in the unbelievable and reconciler of contradictions based on the best arguments that can be made to justify it. But ultimately it rests on absurdity as the main doctrine for its existence. The doctrine being that its very lack of logic is precisely that which gives it power. An idea which in a unique kind of way is eminently logical as a methodology of overcoming all objections to that which is inherently nonsensical but not without meaning.

Truth exists to the best of one's ability to express usually in the form of probabilities. If something is eternal it's less likely to be a god but more so a multiverse in which universes flicker in and out of existence; an eternity of processing and re-processing. Based on what we know there's a greater probability of a multiverse existing than any god entity denoted as eternal.