By Rabbi Eliezer Lerner
The Gemara Brachot (20b) states that the mitzvah of Kiddush is a Torah obligation derived from the pasuk: "Zachor et Yom HaShabbat L'kadsho". However, the nature of the mitzvah ofHavdala is unclear. The Rambam (Hilchot Shabbat 29:1) writes that Havdala is also a mitzvah from the Torah, derived from the very same pasuk. Kiddush and Havdala are two parts of the same mitzvah. The Maggid Mishneh comments that there are those who disagree with the Rambam and claim that Havdala is a Rabbinic obligation.
Even according to the Rambam, the Torah obligation of Kiddush and Havdala involves only the recitation of certain ideas. The need to say these brachotover a cup of wine is mandated by Rabbinic decree. (Hilchot Shabbat, 29:1, 6) The Gemara Brachot (33a) relates that originally, the Sages legislated that the mitzvah of Havdala may be performed through davening. Later when the economic status of the Jews improved, it became mandatory to recite Havdala on a cup of wine. Much later, when there was an economic decline, Chazal legislated that Havdala should again be said during davening, but must also be said over wine.