When a person has tzaraas, he is supposed to say to the kohen (14:35) כנגע נראה לי בבית, "Something like a nega (tzaraas) has appeared to me in the house." Notice the כ at the beginning of כנגע. This means that he isn't telling the kohen that he saw a definite nega, but instead that he saw something that appears like a nega. Rashi explains, "Even a Talmid chacham, who knows that it is a nega, shall not make his statement using a decisive expression, saying, 'A nega has appeared to me.' He should say, 'Something like a nega has appeared to me.'"
The Tosfos Yom Tov (Negaim 12:5) writes several explanations why one shouldn't say definitively that it is a nega of tzaraas. Here are a few of the reasons:
- The Mizrachi teaches: He doesn't say that it is tzaraas to honor the kohen, to let the kohen decide whether it is tzaraas or not.
- The Maharal teaches: Chazal say that until the kohen calls it a nega, the tzaraas isn't tamei. It only has the tumah of tzaraas once deemed a tzaraas by a kohen. So, it would be untrue to say it is a nega because it isn't yet.
- Another answer is that the person shouldn’t call it a nega because this will convince the kohen to see it that way.
The Tosfos Yom Tov then writes his own explanation. It is based on the principle that one shouldn't open his mouth to the Satan. It is wiser if he doesn't proclaim that it is a nega because this can cause what he says to occur. A nega can change colors and turn to a lighter shade and then become tahor. By the time the kohen sees the tzaraas, it might be tahor. But by proclaiming that it is tzaraas and that he is undoubtedly tamei, his words might cause the tzaraas to remain. This is as the Gemara (Moed Kattan 18.) says, there ,ברית כרותה לשפתיים lies a power in words, that whatever one says can occur. And this isn't only when one says something negative. The power of speech is very significant, and saying positive things can also cause good things to happen. People tend to complain and say that things aren’t going well. They would be wiser to get into the practice of saying that everything is good. Their words can cause change for the better.
Reb Shlomo Kluger zt'l says that this is the reason we say the יהי רצון on Rosh Hashanah night by the simanim. We verbalize that it will be a sweet year, and our words create that reality. The Gemara (Brachos 60:) states, "One should always say, 'Everything Hashem does is for the good.'"
Once, Reb Akiva came to a city and asked for a place to stay overnight, and no one took him in. He proclaimed, "Everything Hashem does is for the good." He didn't complain. He believed and said that it was all for his benefit. He slept outdoors that night, in the fields outside the city. He had a rooster, donkey, and candle with him. A wind blew out the candle, a cat ate the rooster, and a lion ate the donkey. Reb Akiva said, "Everything Hashem does is for the good."
Thieves came to the city that night, and everyone was taken captive. Reb Akiva was saved because he wasn't in the city and didn't have a donkey, rooster, or candle that would give away where he was staying. Reb Akiva told his students, "Didn't I tell you ‘everything Hashem does is for the good’?"
What was Reb Akiva telling his students?
The Ben Ish Chai (Ben Yohoyada) explains that he was showing them that even if there is a gezeirah for something terrible to occur (and perhaps it was decreed that he, too should be in captivity), by saying that it is good, his positive words can reverse it and it becomes good.
