Theophylact of Ohrid

But this upper room is "furnished," that is, although it is lofty, it contains nothing harsh or proud; on the contrary, it is furnished and smoothed with humility. It is here, in such a mind, I say, that the Passover is prepared for Christ by the two disciples, Peter and John, that is, by action and contemplation, for Peter was fervent and active, while John, as the Theologian, was contemplative.

Commentary on Mark ↗

Jerome

[Daniel 6:10] "Now when Daniel learned of it, that is, of the law which had been enacted, he entered his house, and with the windows in his upper room opened up in the direction of Jerusalem, he continued to bow his knees three times a day and worshipped, and made confession before his God just as he was previously accustomed to do." We must quickly draw from our memory and bring together from all of Holy Scripture all the passages where we have read of domata, which mean in Latin either "walled enclosures" (menia) or "beds" or …

St. Jerome, Commentary on Daniel, CHAPTER SIX ↗

Bede

And he will show you a large upper room furnished and prepared there for us, etc. The large upper room is the spiritual law, which leaving the narrowness of the letter, receives the Savior in a high place. For he who still observes the killing letter, who understands nothing in the lamb but a mere animal, certainly does less of the Passover: because he has not yet learned to grasp the majesty of the spirit in the words of God. …

On the Gospel of Mark ↗