Suffer not thy mouth to cause thy flesh to sin; neither say thou before the angel, that it was an error: wherefore should God be angry at thy voice, and destroy the work of thine hands? Neither say thou before the angel, that it was an error - Nor think of saying "before the cruel angel, who shall exercise authority over thee in the judgment of the great day, that thou didst it through ignorance." - Chaldee. I believe by the angel nothing else is intended than the priest, whose business it was to take cognizance of vows and offerings. See Leviticus 5:4, Leviticus 5:5. In Malachi 2:7, the priest is called the "angel of the Lord of hosts."
Related Commentaries of Ecclesiastes 5:6
Ecclesiastes 5:6
6 Suffer not thy mouth to cause thy flesh to sin; neither say thou before the angel, that it was an error: wherefore should God be angry at thy voice, and destroy the work of thine hands?