Facing the people, with their hands lifted and positioned precisely, the Kohanim perform the special Mitzvah of blessing the congregation. The blessings origin is found in this week's Parsha. May Hashem make His countenance shine upon you and be gracious to you. May the Hashem bless you and guard you - is a blessing of prosperity and life. May Hashem make His countenance shine upon you and be gracious to you - is a blessing of spiritual graciousness, of perceiving Hashem's many blessings.
Blessings are actually prayers.
When we bless someone, in effect we are actually praying on their behalf. But contrary to the popular mis-translation, Mazel does not suggest luck, it refers to an astrological constellation. Arriving in Toronto early, we stopped for lunch at a Kosher restaurant. There we met an elderly gentleman who turned out to be an old Rebbi of mine from my teen years, a real character. Kathy was delighted to meet the famous Rabbi Rivlin and asked him to kindly bless her with health and long life.