John Chrysostom

Again it may be said, that he hath not, who has not truth. But our Lord says that he hath, because he has a lie, for every one whose understanding believes a lie, thinks that he has something.

Catena Aurea by Aquinas ↗

Theophylact of Ohrid

Whoever has zeal and diligence will also be given a reward, but whoever does not have zeal and diligence, even what he thinks he has will be taken from him. For on account of laziness, even that small spark which he formerly had is extinguished in him, just as through diligence it is kindled.

Commentary on Mark ↗

Bede

For whoever has, to him more will be given. And whoever does not have, even what he has will be taken away from him. He said, with full intention, give effort to the word that you hear, by remembering and examining: because whoever has love for the word, even the sense of understanding what he loves will be given to him. But whoever does not have love for hearing the word, even if he seems to excel either by natural talent or by exercise in letters, will enjoy none of the sweetness of true wisdom. …

On the Gospel of Mark ↗