If we fret constantly about having enough food and clothing, we show that we have not yet learned a very basic lesson that nature teaches us: God provides for His creatures" needs. Furthermore God is the heavenly Father of believers. Consequently He will take special care of them. This argument is a minori ad maius, "From the lesser to the greater." This does not mean we can disregard work, but it does mean we should disregard worry. [source][source][source]
Fretting cannot lengthen life any more than it can put food on the table or clothes on the back ( Matthew 6:27). Worry really shortens life. [source][source][source]