56 For in the case of those who are seeking first the kingdom of God and His righteousness, i.e. who are preferring this to all other things, so that for its sake they are seeking the other things, there ought not to remain behind the anxiety lest those things should fail which are necessary to this life for the sake of the kingdom of God. For He has said above, “Your Father knows that you have need of all these things.” And therefore, when He had said, “Seek ye first the kingdom of God and His righteousness,” He did not say, Then seek such things (although they are necessary), but He affirms “all these things shall be added unto you,” i.e. will follow, if you seek the former, without any hindrance on your part: lest while you seek such things, you should be turned away from the other; or lest ye should set up two things to be aimed at, so as to seek both the kingdom of God for its own sake, and such necessaries: but these rather for the sake of that other; so shall they not be wanting to you. For you cannot serve two masters. But the man is attempting to serve two masters, who seeks both the kingdom of God as a great good, and these temporal things. He will not, however, be able to have a single eye, and to serve the Lord God alone, unless he take all other things, so far as they are necessary, for the sake of this one thing, i.e. for the sake of the kingdom of God. But as all who serve as soldiers receive provisions and pay, so all who preach the gospel receive food and clothing. But all do not serve as soldiers for the welfare of the republic, but some do so for what they get: so also all do not minister to God for the welfare of the Church, but some do so for the sake of these temporal things, which they are to obtain in the shape as it were of provisions and pay; or both for the one thing and for the other. But it has been already said above, “You cannot serve two masters.” Hence it is with a single heart and only for the sake of the kingdom of God that we ought to do good to all; and we ought not in doing so to think either of the temporal reward alone, or of that along with the kingdom of God: all which temporal things He has placed under the category of tomorrow, saying, “Take no thought for tomorrow.” For tomorrow is not spoken of except in time, where the future succeeds the past. Therefore, when we do anything good, let us not think of what is temporal, but of what is eternal; then will that be a good and perfect work. “For the morrow,” says He, “will be anxious for the things of itself;” i.e., so that, when you ought, you will take food, or drink, or clothing, that is to say, when necessity itself begins to urge you. For these things will be within reach, because our Father knows that we have need of all these things. For “sufficient unto the day,” says He, “is the evil thereof;” i.e. it is sufficient that necessity itself will urge us to take such things. And for this reason, I suppose, it is called evil, because for us it is penal: for it belongs to this frailty and mortality which we have earned by sinning. Do not add, therefore, to this punishment of temporal necessity anything more burdensome, so that you should not only suffer the want of such things, but should also for the purpose of satisfying this want enlist as a soldier for God.
57. In the use of this passage, however, we must be very specially on our guard, lest perchance, when we see any servant of God making provision that such necessaries shall not be wanting either to himself or to those with whose care he has been entrusted, we should decide that he is acting contrary to the Lord's precept, and is anxious for the morrow. For the Lord Himself also, although angels ministered to Him, yet for the sake of example, that no one might afterwards be scandalized when he observed any of His servants procuring such necessaries, condescended to have money bags, out of which whatever might be required for necessary uses might be provided; of which bags, as it is written, Judas, who betrayed Him, was the keeper and the thief. In like manner, the Apostle Paul also may seem to have taken thought for the morrow, when he said: “Now concerning the collection for the saints, as I have given order to the saints of Galatia, even so do ye: upon the first day of the week let every one of you lay by him in store what shall seem good unto him, that there be no gatherings when I come. And when I come whomsoever you shall approve by your letters, them will I send to bring your liberality unto Jerusalem. And if it be meet that I go also, they shall go with me. Now I will come unto you when I shall pass through Macedonia: for I shall pass through Macedonia. And it may be that I will abide, yea, and winter with you, that you may bring me on my journey wherever I go. For I will not see you now by the way; but I trust to tarry a while with you, if the Lord permit. But I will tarry at Ephesus until Pentecost.” In the Acts of the Apostles also it is written, that such things as are necessary for food were provided for the future, on account of an impending famine. For we thus read: “And in these days came prophets down from Jerusalem to Antioch, and there was great rejoicing. And when we were gathered together, there stood up one of them named Agabus, and signified by the Spirit that there should be great dearth throughout all the world: which came to pass in the days of Claudius Cæsar. Then the disciples, every one according to his ability, determined to send relief to the elders for the brethren which dwelt in Judæa, which also they did by the hands of Barnabas and Saul.” And in the case of the necessaries presented to him, wherewith the same Apostle Paul when setting sail was laden, food seems to have been furnished for more than a single day. And when the same apostle writes, “Let him that stole steal no more: but rather let him labour, working with his hands the thing which is good, that he may have to give to him that needs;” to those who misunderstand him he does not seem to keep the Lord's precept, which runs, “Behold the fowls of the air; for they sow not, neither do they reap, nor gather into barns;” and, “Consider the lilies of the field, how they grow; they toil not, neither do they spin;” while he enjoins the parties in question to labour, working with their hands, that they may have something which they may be able to give to others also. And in what he often says of himself, that he wrought with his hands that he might not be burdensome; and in what is written of him, that he joined himself to Aquila on account of the similarity of their occupation, in order that they might work together at that from which they might make a living; he does not seem to have imitated the birds of the air and the lilies of the field. From these and such like passages of Scripture, it is sufficiently apparent that our Lord does not disapprove of it, when one looks after such things in the ordinary way that men do; but only when one enlists as a soldier of God for the sake of such things, so that in what he does he fixes his eye not on the kingdom of God, but on the acquisition of such things.
Source: Our Lord's Sermon on the Mount (New Advent)