The Mishna teaches that a number of seemingly innocuous expressions should be avoided. Here are two examples:
1. Yevarkhukha tovim – “May the good bless You” – is seen as a form of heresy.
Rashi explains the heresy as stemming from the fact that we should be including all of the Jewish people in praise of God, not merely good people. The Rid, Rabbeinu Yehonatan and others suggest that this teaching is based on the passage in Sefer Yirmiyahu (44:17) from where we can see that tovim can be interpreted as seve’im – satiated – and the heresy stems from the suggestion that only those people who are fully satisfied need to bless God, while those less fortunate do not. Another approach is suggested by the Meiri, who understood tovim to mean the angels – making the expression Yevarkhukha tovim mean that only heavenly creatures praise God and, as such, removing Him from connection with this world.
2. Al kan tzipor yagi’u rahamekha – “Your mercy is extended to a bird’s nest” – is a statement that should not be said. (See Devarim 22:6 for the source of such a statement.)
Two reasons for this are posed by the Gemara. One suggestion is that this statement will create envy among the creations, i.e. that it appears as though God shows favoritism to one creature over the rest.
The other opinion in the Gemara is that one who says this is, in effect, suggesting that God’s commandments are based on mercy, when, in fact, they are gezerot – laws whose reasoning is not ours to understand. This statement, which appears to limit any study of te’amei ha-mitzvot (the “taste of,” or reasoning behind, the commandments), is the subject of much discussion among Jewish thinkers and philosophers. In response to this argument, the Meiri, for example, explains that the intent of the Gemara is not to deny the mercy of a given commandment; rather it is to emphasize that the end goal is not God’s mercy in this case, but an educational goal of teaching us mercy by means of performing this mitzva.
The Yerushalmi suggests yet another approach – that this statement puts limits on God’s abilities in that He shows mercy only to birds and similar creatures.