Notice this sentece from the text: "humilitate quadam ac modestia, nondum iter hoc ingressos" what was keeping people from the "path" was "humility and modesty" That right there is the spark of a great fire.
Medieval artists were very often anonymous. People were supposed to work for the glory of god, not of themselves. Statements like these were the first steps towards rekindling personal pride. This might seem unimportant, but it is in fact the key to understanding the Renaissance. If you have pride, you are more likely to try to excel and achieve glory through your work and discoveries, you are also less likely to submit to what others say you should think or do (things like "the earth is the center of the universe because I say so, obedience to the Church is your only salvation, humble yourselves like sheep before your shepherd" simply don't work on the proud).
But where could this new mindset find inspiration? What culture valued reason, the beauty of the human body, and questioned everything, even the existence of gods? Well hello there ancient Greece, hello there ancient Rome, nice to meet you again.
TL;DR: Personal pride = bye bye medieval theocracy