"Therefore I say to you, do not worry about your life, what you will eat or what you will drink; nor about your body, what you will put on. Is not life more than food and the body more than clothing? Look at the birds of the air, for they neither sow nor reap nor gather into barns; yet your heavenly Father feeds them. Are you not of more value than they? Which of you by worrying can add one cubit to his stature?
Notice this: Jesus never says 'don't think about tomorrow', He says 'don't worry about tomorrow'. Don't stress out about it. God will take care of you!
Jesus isn't saying 'don't work'. He's saying that God will take care of us, and again, don't stress out.
To answer Jesus' rhetorical questions: we are considered more valuable than the birds, by God (we're made in His image) and people, for the most part (bird-hunting usually isn't a crime, but murder is). Who grows by worrying, is His second rhetorical question. (chirp, chirp). Exactly. Some versions have it as 'life longer' instead of growth. The basic idea: worrying is of no benefit to us.
I was reading a story somewhere about a soldier whose leg was blown off in Iraq. He said that at first, he screamed, but then he realized that screaming wasn't going to help him, so he stopped and took measures to help himself. Worrying is the same way: we do it at first, until (hopefully) we realize that it's not going to help us, and God is going to take care of us.
In His Service,
Response Question: When you look into the sky, and you see a bird flying, what do you think about?