Basically His advise if you will is what good is there in worrying? In other words how does it benefit you? In v.25 He asks is life not more than the temporal (food, clothing and shelter) are we not to live for the eternal? In v.26 He notes, all that God does for nature and how much more will He do for His chosen? Finally in our text, what is it you hope to gain? Will worry and extend our lives?
No matter the situation, no matter the problems of life God is in control and His shoulders are big enough for all our burdens.