But rather seek first the kingdom of God This is another argument for restraining excessive anxiety about food. It argues a gross and indolent neglect of the soul, and of the heavenly life. Christ reminds us that there is the greatest inconsistency in men, who are born to a better life, being wholly employed about earthly objects. He who assigns the first rank to the kingdom of God, will not carry beyond moderation his anxiety about food. Nothing is better adapted to restrain the wantonness of the flesh from breaking out in the course of the present life, than meditation on the life of the heavens. The word righteousness may be either understood as applying to God, or to the kingdom: for we know that the kingdom of God consists in righteousness, (Romans 14:17,) that is, in the newness of spiritual life. All other things shall be added This means, that those things which relate to the present life are but favorable appendages, and ought to be reckoned greatly inferior to the kingdom of God

But seek ye first the kingdom of God - See on Matthew 3:7 (note).
His righteousness - That holiness of heart and purity of life which God requires of those who profess to be subjects of that spiritual kingdom mentioned above. See on Matthew 5:20 (note).
The seventh reason against these worldly cares and fears is - because the business of our salvation ought to engross us entirely: hither all our desires, cares, and inquiries ought to tend. Grace is the way to glory - holiness the way to happiness. If men be not righteous, there is no heaven to be had: if they be, they shall have heaven and earth too; for godliness has the promise of both lives. 1-Timothy 6:3.
All these things shall be added unto you - The very blunt note of old Mr. Trapp, on this passage, is worthy of serious attention. All things shall be added. "They shall be cast in as an overplus, or as small advantages to the main bargain; as paper and pack-thread are given where we buy spice and fruit, or an inch of measure to an ell of cloth." This was a very common saying among the Jews: "Seek that, to which other things are necessarily connected." "A king said to his particular friend, 'Ask what thou wilt, and I will give it unto thee.' He thought within himself, 'If I ask to be made a general I shall readily obtain it. I will ask something to which all these things shall be added:' he therefore said, 'Give me thy daughter to wife.' This he did knowing that all the dignities of the kingdom should be added unto this gift." See in Schoettgen.
To this verse, probably, belong the following words, quoted often by Clement, Origen, and Eusebius, as the words of Christ: αιτειτε τα μεγαλα, και τα μικρα υμιν προστεθησεται· και αιτειτε τα επουρανια, και τα επιγεια προστεθησεται υμιν. "Ask great things, and little things shall be added unto you; ask heavenly things, and earthly things shall be added unto you."

But seek first the kingdom of God,.... Meaning either the Gospel, and the ministration of it; in which sense this phrase is often used, see Matthew 21:43 and which is diligently to be sought after, and into; to be constantly attended on, and to be preferred to our necessary food, to raiment, or riches, or any enjoyment of life: or else the kingdom of glory, which is prepared by God, and is his gift; for which he makes his people meet here, and will introduce them into it hereafter.
And his righteousness; the righteousness of God, which is revealed in the Gospel, and is what gives a right and title to the kingdom of heaven. This is not the righteousness of man, but of God; and is no other than the righteousness of Christ; so called, because he is God who has wrought it; it is what God approves of, accepts, and imputes, and which only can justify in his sight, and give an abundant entrance into his kingdom and glory. Heaven is to be sought for in the first place, as the perfection of the saints' happiness; and Christ's righteousness is to be sought for, and laid hold on by faith, as the way and means of enjoying that happiness; without which, there will be no entering into the kingdom of heaven.
And all these things shall be added unto you: of the free bounty, goodness, and liberality of God, without your thought and care, and much less merit; even "all these things", meat, drink, clothing, or whatsoever worldly sustenance else is necessary for you: which are not parts of the happiness of saints, only appendages thereunto; which they have over and above what they are, or should be chiefly seeking after. The Hebrews (r) say,
"that no good sign will be shown to Israel, until they return and "seek" three things: "afterwards the children of Israel shall return and seek the Lord"; , "this is the kingdom of heaven"; and "David their king", according to its literal sense; "and shall fear the Lord and his goodness"; this is the house of the sanctuary, as it is said, "this goodly mountain", and Lebanon.''
(r) Jarchi & Kimchi, in Hosea. iii. 5.

But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you--This is the great summing up. Strictly speaking, it has to do only with the subject of the present section--the right state of the heart with reference to heavenly trod earthly things; but being couched in the form of a brief general directory, it is so comprehensive in its grasp as to embrace the whole subject of this discourse. And, as if to make this the more evident, the two keynotes of this great sermon seem purposely struck in it--"the KINGDOM" and "the RIGHTEOUSNESS" Of the kingdom--as the grand objects, in the supreme pursuit of which all things needful for the present life will be added to us. The precise sense of every word in this golden verse should be carefully weighed. "The kingdom of God" is the primary subject of the Sermon on the Mount--that kingdom which the God of heaven is erecting in this fallen world, within which are all the spiritually recovered and inwardly subject portion of the family of Adam, under Messiah as its Divine Head and King. "The righteousness thereof" is the character of all such, so amply described and variously illustrated in the foregoing portions of this discourse. The "seeking" of these is the making them the object of supreme choice and pursuit; and the seeking of them "first" is the seeking of them before and above all else. The "all these things" which shall in that case be added to us are just the "all these things" which the last words of Matthew 6:32 assured us "our heavenly Father knoweth that we have need of"; that is, all we require for the present life. And when our Lord says they shall be "added," it is implied, as a matter of course, that the seekers of the kingdom and its righteousness shall have these as their proper and primary portion: the rest being their gracious reward for not seeking them. (See an illustration of the principle of this in 2-Chronicles 1:11-12). What follows is but a reduction of this great general direction into a practical and ready form for daily use.

Seek ye first the kingdom of God. The promise is made that if we seek it first, and its righteousness, all earthly wants will be supplied. The condition demands, 1. That we seek the kingdom first in point of time. Some propose to secure a competence, and after they have gained it, they will serve God. 2. We must make it first in importance. Everything else must give way before its demands. 3. It must be first in our affections, have our whole hearts. We must "love the Lord our God with the whole heart" (Matthew 22:37).
His righteousness. The righteousness that God bestows upon those who are in the Kingdom, Christ's righteousness, the forgiveness of sins in his name.

Seek the kingdom of God and his righteousness - Singly aim at this, that God, reigning in your heart, may fill it with the righteousness above described. And indeed whosoever seeks this first, will soon come to seek this only.