This question draws the conclusion of the one before it. If worry cannot accomplish even the smallest thing, it makes no sense to worry about bigger things. Gill explains "the least" as adding "one moment" to a person's days. He then reasons that if life cannot be lengthened a moment by worry, it cannot be kept going for months and years by worry either. Jesus is moving His disciples from the plain fact of their limits to the folly of anxious care.

The answer is clear without words: there is no good reason. Jesus goes on to the lilies, which "toil not" and "spin not," yet are dressed more finely than "Solomon in all his glory" (Luke 12:27). Then He tells them, "seek not ye what ye shall eat, or what ye shall drink, neither be ye of doubtful mind" (Luke 12:29), and "rather seek ye the kingdom of God" (Luke 12:31).

The "rest" refers back to what Jesus named in Luke 12:22-23: what to eat and what to wear, the needs of "life" and "body." "Take ye thought" is the same verb as in Luke 12:22 and Luke 12:25, which the interlinear glosses "being anxious." The ESV therefore reads, "why are you anxious about the rest?"

This saying appears only in Luke. Matthew's parallel moves straight from the cubit to clothing (Matthew 6:27-28).

Jesus' argument runs from small to great. If we cannot manage the least thing, we certainly cannot manage everything else, so the whole weight must rest on God. Matthew Henry says these arguments are "for our encouragement to cast our care upon God, which is the right way to get ease."

The goal is not to leave the disciples feeling small but to turn them toward their Father. A few sentences later Jesus says, "Fear not, little flock; for it is your Father's good pleasure to give you the kingdom" (Luke 12:32). Admitting our limits opens room to receive what God gives.