Why 'Look at the birds'?

I was given this verse as part of a meditation at a Catholic Youth Festival last summer - and it has just stayed with me. And that was the message I took away from the Festival. Don't be afraid. There is lots we do worry about, lots we could worry about, but surprisingly little that we should worry about.

The passage goes on:

So do not start worrying: 'Where will my food come from? or my drink? or my clothes?' ... Your Father in Heaven knows you need all these things. Instead be concerned about everything else with the Kingdom of God and with what he requires of you, and he will provide you with all these other things. So do not worry about tomorrow; it will have enough worries of its own...
Mt 6: 31-34

Worrying about things takes a lot of time and energy. If I worried about everything, I would never do anything. So, I should only worry about the really important things. Things like 'Am I doing the right thing?', 'What is God calling me to do in the present moment?', or 'How can I best be myself?'. God takes care of the rest, even if it doesn't always seem obvious.