What Jesus means by seeking God's kingdom and righteousness as of first importance
may be judged in part from Matthew 6:25-34 and in part from Jesus' other teaching in the Gospel of Matthew, which I urge us worrying Christians to read carefully. Here, suffice it to say we are to love God and our neighbor, trust God that He has our best interest in mind, and that God intends that we learn though our trials to trust Him rather than worry.