Q. Why do we say L’Chayyim when we have a drink?
In moderation it is an aid to health; the sages used to say when they took a drink, “Wine and health to the rabbis and their students!” (Shabbat 67b).
But wine can also cause problems. According to the Zohar, the forbidden fruit that Adam ate was grapes. Noah sinned because of wine (Gen. 9:21). The sins caused by taking too much wine are usually sins of speech – “When wine comes in, discretion leaves” say the sages (Eruvin 65a; cf. Prov. 23:29).
Hence when we take a drink our L’Chayyim indicates our intention to conduct ourselves correctly and not commit an averah.
Another explanation is that wine was given to deaden the senses – Solomon says, “Give strong drink to him that is about to perish and wine to the bitter in soul” (Prov. 31:6). A person being led out to execution was given wine; saying L’Chayyim shows that a person is not a condemned criminal (Sanh. 43a).
Wine was also given to mourners, and a L’Chayyim signifies that we are happy and not sad.