Jamieson, Fausset and Brown on Isaiah 58:3

3. 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--(Le 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 (Ne 5:1-5, 8-10, &c.).