Most likely, people went around with long faces/a demeanour that encouraged others to ask what was wrong so that they could tell them that they were fasting.1 It may be that people also wore different clothes and put ashes on their head (see Daniel 9:3; Jonah 3:5),2 or afflicted themselves in some other way (Leviticus 23:32).3 By making sure that everyone knew you were fasting, it was no longer a righteous activity done for the purpose of drawing near to God,4 but an act to win the approval and praise of your fellow man.5
16 “And when you fast, do not look gloomy like the hypocrites, for they disfigure their faces that their fasting may be seen by others. Truly, I say to you, they have received their reward.