Why We Must Make Authoritative Figures Only Those Who Are of the Church

It is true that we can find and relate to things coming from different sources. The Church Fathers and Desert Saints found interesting quotes to apply to life even in ancient works written by idolaters. However, we must be extremely careful how we can use such information and we must never make those that are outside of the Church authoritative figures. We cannot say that since such and such (who is outside the Church) said it, it must be true or adhered to. Like bees, we can collect some honey (thought arousing, etc.) from different sources, however, that never makes the sources holy nor gives them any stance.
Clearly, as the below quote says, no one who refuses the community of the Saints and salvation (which is the Church) is holy. They can be good people with good insight in some particular thing but if they differ with the belief of the Church in any matter, they are wrong. They are never holy because the Church is the source of all holiness.

“Why must one obey the Church and not some man whose thinking is opposed to that of the Church, eminent or intellectually gifted though that man may be? Because the Church was founded by the Lord Jesus Christ and is guided by the inspiration of the Holy Spirit of God. Also because the Church signifies the community of the saints, an orchard of choice, fruit-bearing trees. If a man remains opposed to the community of the saints, that means that he is unholy. Why, therefore, listen to him? The Church is an enclosure, says the wise Chrysostom. If you are within, the wolf cannot enter, but if you stray outside, the wild beasts will get you… Do not wander from the Church; there is nothing more impregnable than the Church. She is your hope and your salvation. She is higher than the heavens, firmer than rock, wider than the world; she never grows old, but is forever renewing her youth.”
Source: Prologue, Jan 1