Isaiah 58:3

Here we have, I. The displeasure which these hypocrites conceived against God for not accepting the services which they themselves had a mighty opinion of (Isa 58:3): Wherefore have we fasted, say they, and thou seest not? Thus they went in the way of Cain, who was angry at God, and resented it as a gross affront that his offering was not accepted. Having gone about to put a cheat upon God by their external services, here they go about to pick a quarrel with God for not being pleased with their services, as if he had not done fairly or justly by them. Observe, 1. How they boast of themselves, and magnify their own performances: "We have fasted, and afflicted our souls; we have not only sought God daily (Isa 58:2), but have kept some certain times of more solemn devotion." Some think this refers to the yearly fast (which was called the day of atonement), others to their arbitrary occasional fasts. Note, It is common for unhumbled hearts to be proud of their professions of humiliation, as the Pharisee (Luk 18:12), I fast twice in the week. 2. What they expected from their performances. They thought God should take great notice of them, and own himself a debtor to them for their services.

— Matthew Henry's Concise Commentary (public domain)

Wherefore--the words of the Jews: "Why is it that, when we fast, Thou dost not notice it" (by delivering us)? They think to lay God under obligation to their fasting (Psa 73:13; Mal 3:14). afflicted . . . soul-- (Lev 16:29). Behold--God's reply. pleasure--in antithesis to their boast of having "afflicted their soul"; it was only in outward show they really enjoyed themselves. GESENIUS not so well translates, "business." exact . . . labours--rather, "oppressive labors" [MAURER]. HORSLEY, with Vulgate, translates, "Exact the whole upon your debtors"; those who owe you labor (Neh 5:1-5, Neh 5:8-10, &c.).

— Jamieson-Fausset-Brown Commentary (public domain)