A Jew is commanded to recite one hundred blessings each and every day (Menachot 43b). We need constant reminders to ensure that we recognize the blessings of G-d and to remind ourselves that in all of our actions we are to reflect the Divine image. While most of the brachot we make consist of man acknowledging G-d as the master of the world, the priestly blessings are an exception to this pattern. In this particular blessing the Torah commands man to bless his fellow man.
The Netziv, in his commentary on Chumash, explains that the first verse of the priestly blessing "May G-d guard you and protect you" has different connotations for different types of people. For one engaged in business, we ask G-d to bless us with great material success, yevarechecha, and that such success does not destroy our character, veyishmerecha.