This is one consideration, but there is another no less important. And what is this? Christ having come to earth wished to instruct men in all virtue: now the instructor teaches not only by word, but also by deed: for this is the teacher's best method of teaching. A pilot for instance when he makes the apprentice sit by his side shows him how he handles the rudder, but he also joins speech to action, and does not depend upon words alone or example alone: in like manner also an architect when he has placed by his side the man who is intended to learn from him how a wall is constructed, shows him the way by means of action as well as by means of oral teaching; so also with the weaver, and embroiderer, and gold refiner, and coppersmith—and every kind of art has teachers who instruct both orally and practically.
Inasmuch then as Christ Himself came to instruct us in all virtue, He both tells us what ought to be done, and does it. “For,” he says, “he who does and teaches the same shall be called great in the kingdom of heaven.” Now observe; He commanded men to be lowly-minded, and meek, and He taught this by His words: but see how He also teaches it by His deeds. For having said “Blessed are the poor in spirit, blessed are the meek,” He shows how these virtues ought to be practised. How then did He teach them?
He took a towel and girded Himself and washed the disciples' feet. What can match this lowliness of mind? For He teaches this virtue no longer by His words only but also by His deeds. Again He teaches meekness and forbearance by His acts. How so? He was struck on the face by the servant of the high priest, and said “If I have spoken evil bear witness of the evil: but if well why do you smite me?” He commanded men to pray for their enemies: this also again He teaches by means of His acts: for when He had ascended the cross He said “Father forgive them for they know not what they do.” As therefore He commanded men to pray so does He Himself pray, instructing you to do so by his own unflagging utterances of prayer.
Again He commanded us to do good to those who hate us, and to deal fairly with those who treat us despitefully: and this He did by his own acts: for he cast devils out of the Jews, who said that He Himself was possessed by a devil, He bestowed benefits on His persecutors, He fed those who were forming designs against Him, He conducted into His kingdom those who were desiring to crucify Him. Again He said to His disciples “Get you no gold nor silver neither brass in your purses,” thus training them for poverty: and this also He taught by His example, thus saying, “Foxes have holes, and the birds of the air have nests, but the Son of man has not where to lay His head.” And He had neither table nor dwelling nor anything else of that kind: not because He was at a loss to obtain them, but because He was instructing men to go in that path.
After the same manner then he taught them also to pray. They said to Him “Teach us to pray.” Therefore also He prays, in order that they may learn to pray. But it was necessary for them not merely to learn to pray but also how they ought to pray: for this reason He delivered to them a prayer in this form: “Our Father which art in Heaven hallowed be your name, Your kingdom come: Your will be done, as in Heaven, so on earth. Give us this day our daily bread: and forgive us our debts as we also forgive our debtors: and lead us not into temptation:” that is into danger, into snares.
Since then He commanded them to pray “lead us not into temptation,” He instructs them in this very precept by putting it in practice Himself, saying “Father if it be possible, let this cup pass away from me,” thus teaching all the saints not to plunge into dangers, not to fling themselves into them but to wait for their approach, and to exhibit all possible courage, only not to rush forwards themselves, or to be the first to advance against terrors. Why so, pray? Both to teach us lowliness of mind, and also to deliver us from the charge of vainglory.
On this account it is said also in this passage that when He had spoken these words “He went away and prayed:” and after He had prayed He speaks thus to His disciples “Could ye not watch with me one hour? Watch and pray that you enter not into temptation.” Do you see He not only prays but also admonishes? “For the Spirit indeed is willing,” He said, “but the flesh is weak.” Now this He said by way of emptying their soul of vanity, and delivering them from pride, teaching them self-restraint, training them to practice moderation.
Therefore the prayer which He wished to teach them, He Himself also offered, speaking after the manner of men, not according to His Godhead (for the divine nature is impassable) but according to His manhood. And He prayed as instructing us to pray, and even to seek deliverance from distress; but, if this be not permitted, then to acquiesce in what seems good to God. Therefore He said “Nevertheless not as I will but as You will:” not because He had one will and the Father another; but in order that He might instruct men even if they were in distress and trembling, even if danger came upon them, and they were unwilling to be torn from present life, nevertheless to postpone their own will to the will of God: even as Paul also when he had been instructed practically exhibited both these principles; for he besought that temptations might be removed from him, thus saying “For this thing I besought the Lord thrice:” and yet since it did not please God to remove it, he says “Wherefore I take pleasure in infirmities, in insults, in persecutions.” But perhaps what I have said is not quite clear: therefore I will make it clearer. Paul incurred many dangers and prayed that he might not be exposed to them. Then he heard Christ saying “my grace is sufficient for you, for my strength is made perfect in weakness.” As soon then as he saw what the will of God was, he in future submitted his will to God's will. By means of this prayer then Christ taught both these truths, that we should not plunge into dangers, but rather pray that we may not fall into them; but if they come upon us we should bear them bravely, and postpone our own will to the will of God. Knowing these things then let us pray that we may never enter into temptation: but if we do enter it let us beseech God to give us patience and courage, and let us honour His will in preference to every will of our own. For then we shall pass through this present life with safety, and shall obtain the blessings to come: which may we all receive by the favour and lovingkindness of our Lord Jesus Christ, with Whom be to the Father, together with the Holy Ghost, glory, might, honour, now and for ever world without end. Amen.
Source: Homily on the Passage "Father, if it be possible . . ." (New Advent)