Ambrose of Milan : And you find in another passage, "For he that keeps the commandment does not know the wicked word" when it is altogether clear that knowledge of wickedness is not culpable, but association with it is. — Interrogation of Job and David 2.7.27 Didymus the Blind : Whoever knows what is good also knows at the same time what is bad. "To know" here does not mean "to do" but simply "to know about something." Because when the commandment is given to turn away from evil and do good, we must also know evil in order to be able to turn away from it and to choose good. About these things the apostle writes with the following words: "But test everything; hold fast to what is good; abstain from every form of evil." One sees here that whoever tests everything, knows that the good is to be chosen and obeyed and that the evil is to be avoided.… Ecclesiastes means that he who obeys the command does not know an evil word, that is, he does not say that he does not "understand" it, but that he does not "use" it. — COMMENTARY ON Ecclesiastes 236:2 Jerome : "He who obeys the commandment will know no evil; and a wise man will know time and justice. "Notice here in particular that 'he will know no evil' has been written instead of 'he will not suffer' or even 'evil will not be in him'. Likewise it has also been written about the Saviour, "for he has made him to be sin for us, who knew no sin." [II Cor. 5, 21.] Instead of 'evil' too Symmachus interprets this phrase as saying, "he who keeps the commandment will experience no wickedness". But he teaches that we should keep the command of a king, and know why and when he orders. — Commentary on Ecclesiastes