Theophylact of Ohrid

The Lord urges the disciples to vigilance. Take heed, He says, what you hear; do not let anything I have said pass you by. "With what measure you mete, it shall be measured to you," that is, to the degree that you are attentive, to that degree you will also receive benefit. To the listener who is always attentive, and moreover to the highest degree, God will also give a great reward, while for the sluggish person the profit of recompense will be proportionate.

Commentary on Mark ↗

Cyprian

That when we have received a wrong, we must remit and forgive it. In the Gospel, in the daily prayer: "Forgive us our debts, even as we forgive our debtors." Also according to Mark: "And when ye stand for prayer, forgive, if ye have ought against any one; that also your Father who is in heaven may forgive you your sins. But if ye do not forgive, neither will your Father which is in heaven forgive you your sins." Also in the same place: "In what measure ye mete, in that shall it be measured to you again."

Treatise XII Three Books of Testimonies Against the Jews ↗

Bede

And he said to them: Take heed what you hear. With the measure you use, it will be measured to you, and more will be added to you. If you diligently (he says) strive to do all the good you can, and to share it with your neighbors: divine grace will assist you, both presently, by giving you the understanding to grasp higher matters, and the ability to accomplish worthier deeds; and in the future, beyond what you know to hope for, it will truly add to you the gifts of eternal recompense.

On the Gospel of Mark ↗