Ecclesiastes 5:6
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? 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?
To suffer the mouth to cause the flesh to sin is to let careless speech lead into breaking a vow, so that a person's own words bring sin and guilt and judgment by causing failure to fulfill what was pledged. The angel before whom the excuse is made is the heavenly angel, the messenger and angel of God who listens to the words, for such vows are made not only before men but before him. To say before the angel that it was an error is to claim afterward that the promise was made by mistake and to dismiss the vow, which must not be done and does not remove the obligation. To promise and then grumble and murmur and withdraw the pledge, while charging that God's servants deceived and pressured out an unjust promise, is itself to sin by one's own mouth and to call the vow a mistake before the angel. Vows pledged to God must be paid without delay, and it is better not to vow than to vow and fail to pay.
The verse applies to solemn pledges made to God, including promises to give for His cause, especially neglected vows and unpaid pledges, and to fail to fulfill them violates duty. God holds men accountable for vows, and those who hold neglected vows and unpaid pledges must settle their claims to Him, for an account will be rendered to God. God is angry at such a voice and answers by destroying and frustrating the work of the hands, withholding blessing and the ability to pay and bringing ruin upon the work.