It is vain. It brings no acknowledgment or reward. The Latin and Greek Versions have, "He is vain who serveth God." Have kept his ordinance (charge). Have done what he ordered. They are either wilfully deceiving themselves and others by pretending an obedience which they never really paid; or they think that the outward observance of certain legal requirements is all that is required.
Some think that an interval of time separates this from the last section, and that meanwhile they had made some efforts at improvement, expecting, how. ever, immediate results in added blessings; and as these did not come as quickly as they hoped, they relapsed into their old distrust.
Have walked mournfully; i.e. in mourning apparel, as if fasting and mourning for sin (Psalms 35:13, Psalms 35:14; Job 30:28). Septuagint, "Why went we as suppliants ( ἱκέται)?" Before the Lord. Out of reverence and awe of Jehovah.
They attributed a certain virtue to voluntary fasts, without any consideration of the spirit in which they were observed (see the reproof of such formal observances in Isaiah 58:4, etc.).