Jerome : "When you make a vow to God, do not delay paying it, for He has no liking for fools; what you vow, pay. Better that you not vow at all, than that you vow and not pay. "A simple man does not need understanding by interpretation. It is better not to promise than not to keep promises, since they displease God and are numbered among fools, who do not fulfil their vows. But since he says, "There is no will in fools" underneath we hear "of God", like the word of the apostle, who says, "and just as there was no will, that I should now come to you" [I Cor. 16, 12.]. For even if we want to say something more inquiring, it is taught to a Christian, that he should fulfil his faith by work, and not be like the Jews, who pledge and say, "we will do all that God commands" [Ex. 24, 3.], and yet worship idols. And afterwards they beat those slaves and cast stones at them, and immediately killed the very son of the father of their house. It is better therefore to hold a doubtful opinion for a while, which is easy to say in words, but difficult to put into practice. For the slave, who knows the will of his God and will not do it will be defeated by many. — Commentary on Ecclesiastes