Parsha Mitzvot: Shofetim: Mitzvah 496 – Concept 252
“The first of your grain, wine, and oil, and the first of your shearing of your flock shall you give him.” (Deuteronomy 18:4) We are commanded to set aside terumah Gedola for the Kohen. (Rambam, Hilchot Terumah)
The advantage of the “Reishit,” the first, is that it makes an impression of holiness on the rest. When there is more left over after the “First” has been separated, it reminds us that whatever we currently have left in our possession is a reflection of the holiness of that “First.” – Rabbi Yitchak Meir of Gur – Chiddushei HaRim
We can always use the first, whether the first moments of Shabbat, or the first food that we eat to change the tenor of all that follows, even to the point of making everything holy by the way we begin.