The havdalah ceremony marks the transition from a sacred day (most often, Shabbat) to a less sacred day (most often, a weekday; sometimes, a holiday). It begins with a number of introductory verses which emphasize how
G-d will protect us during the coming week. It is followed by blessings over wine, spices, and light. And it concludes with this blessing:
Blessed are You, o Lord our G-d, King of the Universe, who makes a distinction between sacred and secular, between light and darkness, between the people of Israel and other peoples, between the seventh day and the six workdays. Blessed are You, o Lord, who makes a distinction between sacred and secular.
The Torah is insistent on making distinctions. It is seen as an essential precondition for achieving holiness. The rabbis, picking up on this, looked for ways to keep us mindful of the importance of making distinctions. They understood that distinction is based on perception. Hence the mention of light and darkness in the final berachah.
But they went beyond this, by ensuring that every one of our senses is engaged when we say this blessing of distinction, We feel the wine cup; we taste the wine; we smell the spices; we see the light (and the darkness—that’s one of the reasons we put our hands up to the light, to heighten the distinction); we hear the blessing. And on top of all those physical senses, we use our mind to recognize the distinctions, and our heart to discern their meaning.