The Sermon on the Mount is "the gospel of the kingdom"(Matthew 4:23). It is the constitution of the Kingdom of God. It is the essence of who the King longs for His citizens to be.
The theme of the sermon is found in Matthew 6:33. "But seek first the kingdom of God and His righteousness, and all these things shall be added to you" (NKJV). Jesus would have His loyal subjects be about the business of seeking "in order to find" (Thayer's) the "rule" (Strong's) of God and His righteousness. To seek the rule of God and His righteousness involves character (5:3-10), being salt and light (5:13-16), righteousness (5:17-20), issues of the heart (5:21-48), good deeds (6:1-4), prayer (6:5-15), fasting (6:16-18), laying up treasures in Heaven (6:19-21), sight (6:22-23), single-mindedness (6:24), trust (6:25-34), judgment (7:1-6), asking, seeking, knocking (7:7-12), the narrow way (7:13-14), fruitbearing (7:15-20), knowing the Lord (7:21-23), and building on the Rock (7:24-27).
I am to seek "first" the kingdom and the righteousness of God. "First" means, well, first. Not second. Not third or fourth. "First" means first in "time, place, order, or importance" (Strong's).
The King of the Kingdom is worthy of first place. Put Him first in your life. Seek first His kingdom and His righteousness. If you do, everything will be all right.
Jason Cicero