This verse is the beginning of an argument, a piece of logic, by Jesus. When He later repeats, “Take no anxious thought,” He is referring to the thought begun here. It is what is called an argument from the greater to the lesser—since God gave us our lives and bodies in the first place, and since He has called us, He will also sustain us.
Has He provided evidence of this? He did it for Israel in the wilderness. God delivered them from Egypt. God did great things there, signs and wonders. He divided the Red Sea. Since He did those great things, would He then fail to provide them with food and water? The same argument goes for our calling. Since He gave us life and breath, and since He called us, Jesus argues, He will also sustain us. Take no anxious thought for what you will eat, what you will drink, or what you will wear. So He who gave us the greater, life and body, will also give us the lesser, food and clothing. So Jesus is saying, "Do not confuse your priorities."
John W. Ritenbaugh
The Christian and the World (Part 8)