The Book of Devarim consists mainly of the speeches that Moshe Rabbenu delivered to Beneh Yisrael before his passing. In the first several parashiyot , Moshe reviews some of the events that took place after Beneh Yisrael left Egypt, placing particular emphasis on the sins that they committed. He speaks at length about the sin of the golden calf and the sin of the spies. He also mentions the instances when Beneh Yisrael complained in the desert, and briefly notes also the revolt by Korah. As Moshe prepared to leave this world, in his "farewell address," he reprimanded the people for the mistakes they made, so that they would not repeat these mistakes. The Midrash describes Moshe reprimanding the people by bringing a pasuk from the Book of Mishleh (28:23): מוכיח אדם אחרי חן ימצא ממחליק לשון . Literally, this means, "He who reprimands a person after Me will find more favor than a slick-tongued person." The Midrash states that this refers to Moshe, who reprimanded the people "after Me," in the proper way, and so his words – despite being critical – found favor in the people's eyes, more so than the words of somebody with a "slick tongue," who has mastered the art of rhetoric. Moshe, as we know, had difficulty speaking. He was not "slick-tongued." Nevertheless, his words of rebuke were effective, and he "found favor" with the people despite talking them harshly about the things they had done wrong, because he spoke to them אחרי – "after Me." The commentaries explain that אחרי refers to sincerity, intentions that are purely לשם לשמיים , for Hashem's sake. When we criticize, people can sense whether we do so sincerely, out of a genuine concern for them, or if we criticize with impure motives. They will feel if we are criticizing because we really care about them, or if we're just angry, or if we're just trying to feel superior to them by putting them down, by showing that we're better than them. They know by the way we speak to them if we are sincere or if we have some agenda. If we criticize אחרי , genuinely לשם שמיים , then we will "find favor," the person will be receptive and open to what we have to say. But if our intentions are insincere, if we are just angry, or looking to feel good about ourselves at somebody else's expense, then the person will notice, and is not likely to accept what we have to say. Instead, he will react with hostility and defend himself. Sincerity has power. When we are sincere, people feel it, and respond accordingly. We often feel the need to criticize the people around us – our children, our spouse, other family members, friends, employees, coworkers, etc. And, many times, it is indeed necessary to criticize. But our criticism will be effective and achieve the desired result only if we are truly sincere, if our only intention is to help the person improve, without any hostility, arrogance or agendas. If we speak with even a tinge of disdain, of disrespect, of gloating, of "gotcha," of "I'm better than you," the person is going to feel it, and will reject everything we say. When it comes to criticism, sincerity is everything. It is only when our sole intention is to help the person get better that there is a chance of our words being heeded.