Albert Barnes Commentary Zechariah 7:6

"And when ye eat, and when ye drink, do not ye eat for yourselves, and drink for yourselves?" — Zechariah 7:6 (ASV)

And when you eat and when you drink, is it not you who eat and you who drink? — Conversely, now that after your return you feast for joy, this is no religious act; you have all the good of it, there is no thanksgiving to God. Contrary to the apostle’s saying, “Whether you eat or drink, or whatever you do, do all to the glow of God” (1 Corinthians 10:31).

“He eats and drinks to himself, who receives the nourishments of the body, which are the common gifts of the Creator, without the needy. And anyone fasts to himself, if he does not give to the poor what for the time he withdraws from himself, but keeps it to be thereafter offered to his appetite. Hence, it is said by Joel, sanctify a fast. For to ‘sanctify a fast’ is to show an abstinence worthy of God through other good deeds.”

Let anger cease, quarrels be hushed. For in vain is the flesh worn, if the mind is not refrained from evil pleasures, since the Lord says by the prophet, “Behold, in the day of your fast you find pleasure. Behold, you fast for strife and debate ...” (Isaiah 57:3–4).