Romans 10:8- “But what does it say? The WORD is near you; it is in your mouth and in your heart, that is, the message concerning faith that we proclaim.”
Obstinacy is something I’ve lived, and have been letting go of, so I speak from lessons God has taught me.
Being a person who has appeared strong (heavily masked) yet has been in those dark places of self-doubt and the thoughts of giving up (at the same time) I can see from a different and personal view- into this question of how to reach those who need help (those who are heavily masked.)
Romans 10:15(b)- “…How beautiful are the feet of those who bring good news!” This verse is paralleled in Isaiah 52:7❤️
The answer: it isn’t simply by our own power. See Proverbs 1:16, Isaiah 59:2, Romans 10:21. The verse in Romans 10:15 is Moses speaking to the Isrealites. They believe in God, yet they lacked the bottom-line wisdom because of their obstinacy.
In Romans, lacking in wisdom, is the lacking of declaration that Jesus is Lord (Romans 10:9).
This all comes together to (at least answer part of the question, anyway.)
We have to come to the point of willingness within our own hearts to let go of the obstinate parts of our hearts and fully embrace the GRACE and MERCY which has been bestowed upon us by the blood of Jesus Christ.
So, even believers have to find peace WILLINGLY through Grace first because we are not saved by works, but by Grace alone.
For me this is a huge portion of my Journey. I have to allow God to renew my mind on a daily basis in order for my heart to follow suit. Otherwise, the “fungus” you described can and will grow over and hide the truth.