What is the meaning of Matthew 6:33-34?

33 But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you. 34 Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof. (Matthew 6:33-34 KJV)

Thomas Scott

Verses 33-34: The blessing of the Messiah’s kingdom, righteousness in which his subjects are justified, the grace by which they are sanctified, and the good works in which they should walk, are intended by “the kingdom of God and his righteousness.” our Lord therefore calls his disciples to seek admission into this kingdom by repentance and faith, and every means of grace, and to press forward to the full participation of its privileges, and conformity to the law and example of their righteous King; and also to seek the purity, peace, prosperity, and enlargement of the kingdom, the honor of their Prince, and the good of their fellow-subjects. These must be sought “in the first place,” as the first object, with the first of their affections and time; beginning the year, the month, the week, and the day, with this business, and ordering all things in subservience to it. Then their bountiful Father will add all those things which pertain to this present life without their anxious carefulness; but they who reverse this order, take the way to ruin themselves in respect of this world and that which is to come.—The Christian should not be careful even about the very next day; for it may never arrive  to him: and if it do, it will bring its supports and supplies with it, and thus as it were “take thought for itself.” This should be considered as a merciful appointment of his heavenly Father. He knows that every day brings more trouble and suffering than man can well bear; he therefore allows and commands his children to cast all their care about the future on him. And if any will, notwithstanding, be so absurd as to load themselves with a heavy burden which does not belong to them, and then groan under self-imposed sorrows; they torment themselves, as well as dishonor God, by their folly and unbelief.—This is also applicable to spiritual things. The Christian, while watching, praying, and attending to his duty, is authorized to trust the Lord to give him grace sufficient for future trails and temptations, as well as food sufficient for future temporal wants; and in both cases, “Sufficient for the day is the evil thereof.”