What does Matthew 6:17 mean?

Matthew 6:17 KJV
But thou, when thou fastest, anoint thine head, and wash thy face;

Matthew 6:17 MKJV
But you, when you fast, anoint your head and wash your face,

Matthew 6:17 NKJV
“But you, when you fast, anoint your head and wash your face,

Matthew 6:17 KJV 2000
But you, when you fast, anoint your head, and wash your face;

Interlinear KJV

But /de/ thou, /su/ when thou fastest, /nesteuo/ anoint /aleipho/ thine /sou/ head, /kephale/ and /kai/ wash /nipto/ thy /sou/ face; /prosopon/

Albert Barnes’ Commentary

Verse 17. But thou, when thou fastest, anoint, etc. That is, appear as you do daily. Do not assume any new appearance, or change your visage or dress. The Jews and all neighbouring nations were much in the habit of washing and anointing their bodies. This washing was performed at every meal; and where it could be effected, the head, or other parts of the body, was daily anointed with sweet or olive oil. In a warm climate, exposed to the great heat of the sun, this practice conduced much to health, preserved the skin smooth and tender, and afforded a most grateful sensation and odour. See Mr 7:2,3; Jas 5:14

Mr 6:13; Joh 12:3. The meaning of this whole commandment is, when you regard it to be your duty to fast, do it as a thing expressing deep feeling, or sorrow for sin; not by assuming unfelt gravity and moroseness, but in your ordinary dress and appearance; not to attract attention, but as an expression of feeling towards God, and he will approve and reward it.