I think it is easy to see faith (or a lack thereof) at work in the professing believer.I know that I still don't understand some critical context well enough to tackle the topic of faith yet. I know I am getting closer to faith by not studying the topic and by not discussing it with the people that I did in the past, as I was losing what I believed was faith.
I know that the other children have taught me some things that don't come from our father, even if I don't fully understand what the father did say. I know what faith is NOT, more than I know what it is.
Young children don't understand time. They do not understand that Mommy was alive before they were alive. Some will scream and deny that Mommy was ever a little girl. Others were parrot back that Mommy was a little girl, but have no concept of how that is possible and what that means.
I'm still too little to understand some things. I am focusing on what I do understand and trust I will grow into those other things in time.
I don't know much about this thing called faith, but I have learned to trust God beyond the things that I can understand. I have learned that it is not a sin to wait to understand.
How they treat one another - especially someone with whom they disagree - shows the spirit active in them. Either this is the Spirit of God or the spirit of this world.
My point - faith leads to spiritual truth and spiritual maturity (not "facts" or worldly knowledge of godly topics).