It is for this reason that a person must invest hundreds of times a day in performing mitzvos, in order to attain more emunah, for there is no limit to the levels of emunah that one can attain.
This would be true even if a person were never to fall back in his emunah, and if he were never to see and hear things that diminish his emunah—he would still need to strengthen himself in emunah, for it has no limit. How much more so is this true when we’re constantly bombarded with words, and thoughts, and sights that attack our emunah, and they infiltrate our hearts and minds, and impact our way of thinking—certainly, we must invest in growing our emunah.
And when a Yid merits to develop his feeling of emunah, he can begin to feel: “I just conversed with someone. Everything was fine, but in the last two minutes of the conversation, I deviated from my emunah... my tone of voice went up.... I got a bit perturbed and upset... this wasn’t in keeping with emunah.”
This is the power of the mitzvos of the Torah, which infuse in the heart of a person the knowledge that we should truly feel our emunah and continue steadily growing in it.