Musar for Berakhot 56:4

There are many evils in too much rejoicing and in too much laughter, as for instance one who rejoices when his companion stumbles or when some evil mischance of the tragic happenings that afflict the world comes upon him. And concerning this it is said: "When your enemy falls do not rejoice" (Ibid. 24:17). And there is a joy that is even worse than this — as when a man rejoices because his companion made errors in the Service of the Creator, may He be blessed, or rejoices at the lack of knowledge of his companion. The following parable you should easily understand: a servant who ministers to his king faithfully is pained when he sees people rebelling against his master and abusing him [and he should rebuke them to their faces and let them know the extent of their vile conduct], but when a servant is happy when he sees the service of his master being spoiled and his master's consequent shame, then he is not a faithful servant [he is a comrade to the destroyer and will have to bear his guilt]. And behold Scripture says : "The Lord desires those that revere Him" (Ps. 147:11). And he who rejoices when his companion stumbles — his desire is not like the desire of the Creator, may He be Blessed. Therefore Rabbi Nehunia ben Hakanah prayed : "And let not my fellows err in a point of law and I be happy with this" (Berakoth 28b). Therefore Rabbi Nehunia ben Hakanah prayed to be free from this fault for he saw that it was common that one rejoices in the mistake of his companion in order that he should feel triumphant over his companion and have that fame. And how many important people there are who do not take care in this connection. Therefore, every man whose will is the will of God feels great pain when the will of God is not accomplished by men. A man should pray that even his enemy should serve the Creator, Blessed be He. And he should intend in his prayers — when he comes to the Benedictions of "Thou art Gracious" and "Restore Us" and "Forgive Us" — to include all of Israel, those that love him and those that hate him. And so should it be with all his Benedictions. For how could it be true that he should pray for "the healing of his people Israel" and the other Benedictions, and not want his companion to be healed or become wiser?