What does Matthew 6:27 mean?

Matthew 6:27 KJV
Which of you by taking thought can add one cubit unto his stature?

Matthew 6:27 MKJV
Which of you [by] being anxious can add one cubit to his stature?

Matthew 6:27 NKJV
“Which of you by worrying can add one cubit to his stature?

Matthew 6:27 KJV 2000
Which of you by taking thought can add one cubit unto his stature?

Interlinear KJV

/de/ Which /ek/ /tis/ of you /humon/ by taking thought /merimnao/ can /dunamai/ add /prostithemi/ one /heis/ cubit /pechus/ unto /epi/ his /autos/ stature /helikia/?

Albert Barnes’ Commentary

Verse 27. Which of you by taking thought. The third argument is taken from their extreme weakness and helplessness. With all your care you cannot increase your stature a single cubit. God has ordered your height. Beyond his appointment your powers are of no avail, and you can do nothing. So of raiment. He, by his providence, orders and arranges the circumstances of your life. Beyond that appointment of his providence, beyond his care for you, your efforts avail nothing. Seeing, then, that he alike orders your growth, and the supply of your wants, how obvious is the duty of depending on him, and of beginning all your efforts, feeling that He only can grant you the means of preserving life!

One cubit. The cubit was originally the length from the elbow to the end of the middle finger. The cubit of the Scriptures is not far from twenty-two inches. Terms of length are often applied to life; and it is thought by many to be so here. Thus, it is said, “Thou hast made my days as a handbreadth,” Ps 39:5; “Teach me the MEASURE of my days,” Ps 39:4. In this place it is used to denote a small length. You cannot increase your stature even a cubit, or in the smallest degree. Compare Lu 12:26.

Stature. This word means height. The original word, however, means oftener age, Joh 9:21,23. In these places it is translated age. If this be its meaning here, it denotes that a man cannot increase the length of his life at all. The utmost anxiety will not prolong it one hour beyond the time appointed for death.