But seek first the kingdom of God and His righteousness, and all these things shall be added to you. Therefore do not worry about tomorrow, for tomorrow will worry about its own things. Sufficient for the day is its own trouble. Matthew 6:33-34
It is a pity that this passage (Matthew 6:25-34) is often read on its own in church, isolated from what has gone before. Then the significance of the introductory “Therefore I tell you” is missed. So we must begin by relating this “therefore,” this conclusion of Jesus, to the teaching which has led up to it. He calls us to thought before he calls us to action. He invites us to look clearly and coolly at the alternatives before us and to weigh them up carefully. We want to accumulate treasure? Then which of the two possibilities is the more durable? We wish to be free and purposive in our movements? Then what must our eyes be like to facilitate this? We wish to serve the best master? Then we must consider which is the more worthy of our devotion.
Only when we have grasped with our minds the comparative durability of the two treasures (corruptible and incorruptible), the comparative usefulness of the two eye conditions (light and darkness) and the comparative worth of the two masters (God and mammon), are we ready to make our choice. And only when we have made our choice–for heavenly treasure, for light, for God—”therefore I tell you” this is how you must go on to behave: “do not be anxious about your life…nor about your body…But seek first his kingdom and his righteousness (25, 33).
In In Other words, our basic choice of which of the two masters we intend to serve will radically affect our attitude to both. We shall not be anxious about the one (for we have rejected it), but concentrate our mind and energy on the other (for we have chosen him); we shall refuse to become engrossed in our own concerns, but instead “seek first” the concerns of God.
–John Stott, Christian Counter Culture: The Message of the Sermon on the Mount, p. 159-160