Matthew Henry Commentary Ecclesiastes 5:4-8

"When thou vowest a vow unto God, defer not to pay it; for he hath no pleasure in fools: pay that which thou vowest. Better is it that thou shouldest not vow, than that thou shouldest vow and not pay. Suffer not thy mouth to cause thy flesh to sin; neither say thou before the angel, that is was an error: wherefore should God be angry at thy voice, and destroy the work of thy hands? For in the multitude of dreams there are vanities, and in many words: but fear thou God. If thou seest the oppression of the poor, and the violent taking away of justice and righteousness in a province, marvel not at the matter: for one higher than the high regardeth; and there are higher than they." — Ecclesiastes 5:4-8 (ASV)

When a person made vows rashly, he allowed his mouth to cause his flesh to sin. This refers to a case where a man comes to the priest, pretending that his vow was made rashly and that it would be wrong to fulfill it. Such mockery of God would bring divine displeasure, which might blast what was thus improperly retained.

We are to suppress the fear of man. Set God before you; then, if you see the oppression of the poor, you will not find fault with Divine Providence; nor will you think worse of the institution of government when you see its purposes thus perverted, nor of religion when you see it does not protect people from suffering wrong. But though oppressors may be secure, God will call all to account.