I made sackcloth also my garment - I put on sackcloth. This was often done as expressive of grief and sorrow. See Psalm 30:11, note; Psalm 35:13, note. Compare Isaiah 22:12; Daniel 9:3. In the case here referred to, this was an act of religion; an expression of penitence and humiliation.
And I became a proverb to them - A jest; a subject of derision; a by-word. They ridiculed me for it. Compare 1-Kings 9:7.

I made sackcloth also my garment,.... Though we nowhere read that Jesus put on sackcloth upon any occasion, yet it is not improbable that he did; besides, the phrase may only intend that he mourned and sorrowed at certain times, as persons do when they put on sackcloth: moreover, as the common garb of his forerunner was raiment of camels' hair, with a leathern girdle; so it is very likely his own was very mean, suitable to his condition; who, though he was rich, for our sakes became poor;
and I became a proverb to them; a byword; so that when they saw any person in sackcloth, or in vile raiment, behold such an one looks like Jesus of Nazareth.

Proverb - A proverb of reproach.