Matthew 6:33

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.

— Jamieson-Fausset-Brown Commentary (public domain)