This is all well and good, but how do we measure growth? We can measure the growth of our waistline or our height. How do we measure growth in faith? We hear people say they have grown in faith, but how is that measured?
My waistline is a physical measurement so it can be measured in any unit of distance - inches, centimeters or some other unit.
My weight is a physical measurement so it can be measured in a variety of units - pounds, kilograms, etc.
Both of these are objective measurements. If my weight is 200lb then it's 200lb whether I weigh myself or someone else does it - I weigh the same whether I wear tight-fitting clothes that cling to every lump and bump, or loose fitting clothes that leave my body shape only vaguely defined. I weigh the same whether I suck my tummy in and stand tall, or slouch and let my tummy hang out.
What unit can be used to measure our faith? You keep talking about how it can be measured but unless you can suggest a method of assigning a numerical value to it there's no way of objectively measuring it and therefore no way of measuring it.
I can gauge my own growth in that I know my own struggles, I can see the struggles I've overcome and also see the things that still plague me. I know whether my prayer life is better or worse than it was last week, last month, last year. I can gauge my own progress and conclude whether I'm moving forwards, standing still, or sliding backwards. The trouble is that it's far from objective.
If I want someone else to think I weigh less than I do, I can suck my tummy in and stand tall. I can wear some kind of undergarment that holds my excess in place - it does precisely nothing to change my weight but makes me look slimmer and this, combined with standing tall, may trick someone else into thinking I am leaner and lighter than I really am. The reality isn't changed, but it makes me look better in the subjective judgment of others.
Likewise if I want someone else to think my walk with God is better than it really is there are all sorts of tricks I might pull. Maybe I'll make a point of saying a particularly spiritual-sounding prayer at the Bible study group. Maybe I'll share something that suggests I've got a couple of struggles that are of a particularly spiritual nature, that relate to fine-tuning a gift the others in the group don't have, and couched in sufficiently vague terms that people are invited to speculate just how spiritual my struggle must be. Perhaps I'll do something very charitable when I know someone is watching, with bonus points for doing it when it's not clear that I know they are watching so they think they just happened to notice me doing something very loving. There are all sorts of tricks that might influence someone's subjective judgment but, like the girdle, they do nothing to change the objective reality.
All of this continually points back to the issue of self-examination, even without an objective benchmark against which we can be tested. And it obviously requires honesty because anything else is equivalent of wearing a girdle under my shirt, then looking in the mirror and marvelling at how much weight I've lost this week.