The Gemara (Berachos 29b) relates that Eliyahu hanavi told Rabbi Yehuda to be careful about three things - to always refrain from anger, to never to get drunk, and to recite Tefilas Haderech when traveling. Although these are good pieces of advice, there doesn't appear to be any connection between them. If we analyze the words of Eliyahu hanavi more carefully we will discover that these three suggestions are all part of one message.
Throughout life we are constantly making decisions. In order to decide properly we must understand the differences between the various paths available to us. Sometimes the nuances of distinction are minute, yet the ramifications of not comprehending these differences and arriving at the wrong conclusion can be significant. Chazal incorporated the tefillah of attah chonantanu on motsaei Shabbos in the beracha of attah chonein because, "Im ein de'ah, havdala minayin - if we are lacking in wisdom we cannot possibly distinguish properly. We begin each week with a tefillah asking Hashem to grant us the ability to distinguish between holy and profane in all of our life decisions.
Anger and drunkenness interfere with our decision-making ability. These two states of mind do not enable us to think rationally, and decisions made when under these influences can be tragic. When angry or drunk, one says things that one will inevitably regret, as the ability to recognize inappropriate words and actions is impaired. Overindulgence in any physical pleasures can have the same effect.
Eliyahu was instruction Rabbi Yehuda how to travel safely through life. Just as on the road one must constantly decide which direction to take, so too on the trip through life one faces forks in the road and must differentiate between the correct and incorrect paths. Therefore, the ability to think rationally which enables us to decide appropriately must be present at all times. Just as road rage and drunken driving can be catastrophic, so too on the trip through life the individual who can not think clearly because of anger and alcohol will inevitably make decisions with tragic consequences. It is only by abstaining from these impediments and beseeching Hashem through "Tefillas Haderech" for guidance can a person arrive safely at his destination.
Parshas Shmini is the parsha dedicated to the concept of havdala, the ability to distinguish properly. The kohanim are charged with the mission of, "lehavidl bein hakodesh ubein hachol". Shmini concludes with the obligation upon everyone, "lehavdil bein hatamei ubein hatahor". We must differentiate between what is holy and pure and that which is not. Chazal tell us that sometimes it is very difficult to discern between what is permissible and what is not. The difference between an acceptable and an unacceptable shechita is minuscule. Similarly in other areas, the distinction between holy and profane is sometimes difficult to discern. The kohanim, who must guide the entire nation as to how to differentiate properly, can never do so in a state of drunkenness. The Torah specifically prohibits one who is drunk from serving in the Beis Hamikdash or answering halachic questions, as these areas of activity require one's complete mental capacities.
The pesukim that prohibit kohanim from serving in the Beis Hamikdash while drunk immediately follow the tragedy of Nadav and Avihu. Chazal tell is that they had entered the kodesh hakodoshim after drinking wine. They had lost the ability to discern what was an appropriate form of avodas Hashem and what was not.
Following the deaths of Nadav and Avihu, Moshe realizes that one of the korbanos that he thought was supposed to be eaten was burned, and gets angry at Elazar and Itamar for not treating the korbanos appropriately. Moshe in fact made a mistake, to which he later admitted, in failing to distinguish between korbanos that could be eaten and those that could not. Chazal tell us that even Moshe Rabbeinu's judgment was clouded by anger.
The words of advice given by Eliyahu hanavi to Rabbi Yehuda are as true today as when they were given. As we travel through life we need the siyata diShmaya to make the correct decisions. We must do our part by not clouding our vision through alcohol and the like that dull our senses. To think and act in a rational way, we must also overcome our temptation to become angry. If we do our part and then turn to Hashem by saying Tefillas Hadarech for the path through life, we will hopefully merit lehavidl bein hakodesh ubein hachol ubein hatamei ubein hatahor.