The care which God demands: V. 33. But seek ye first the kingdom of God and His righteousness, and all these things shall be added unto you. To seek, earnestly to covet, to put the whole heart to the gaining of, the kingdom of God, is a most necessary care for the disciples of Christ, for the children of God. For this kingdom is not meat and drink, but righteousness, and peace and joy in the Holy Ghost, Rom. 14, 17. To possess this righteousness, which is well-pleasing to God, to be filled with the fruits of this righteousness, to become rich in truly good works, that is a goal worthy of the Christian’s ambition. Such a constant seeking after purity of heart and holiness of life will incidentally stifle all care and worry of this life. And the little things of this earthly body and life will then come as a matter of course, the main object of the quest having been secured. They will be cast into our laps as an overplus, as an addition to the great bargain which our seeking has gained.
Therefore, once more: V. 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. Each day brings its own evil, for it is an evil world, and the enemies without and within are ever busy devising schemes to beset the heart with care. These conditions must be met with patient cheerfulness, and each problem taken care of as it comes. To add to the difficulties and troubles of the present day by worrying about what the morrow might bring will not ease the situation confronting you now. To restrict all care to the moment when it begins to nag is to conquer it absolutely. It is only the future that brings anxiety. Put each successive day into the hands of God, and it will bring its own help and deliverance from the love of the heavenly Father, Lam. 3, 23.
—Paul E. Kretzmann, on Matthew 6:33-34, hyperlink and color added