From Rabbi Avi Weiss:

Perhaps the most famous blessing is found in this week’s Torah portion. The Birkat Cohanim, the priestly benediction is recited by the priest and by parents to their children every Friday night.(Numbers 6:24-26) The benediction is divided into three sentences each containing two important elements; G-d’s blessing, and a prayer to avoid possible pitfalls of the blessing.

In the first part, the priest states: “May G-d bless you and keep you.” The Sifrei understands this to refer to monetary benefits. But money has the potential to corrupt. Therefore a blessing for money is not complete unless accompanied by an assurance of protection  from its dangers. Hence the last word of the sentence, “May the Lord guard you.”

In the second section, the priest states: “May the Lord cause His light to shine upon you.” The light of G-d is often associated with Torah knowledge (Proverbs 6:23). However, while one can know every word of Torah, one can still lack the ability to interact and engage others in an appropriate manner. Hence, this blessing concludes with the word, vi’chuneka, from the word chen, grace. This last statement is telling us to remain gracious to others because knowledge often makes one insular – even arrogant.

In the final part, the priest states,” May G-d lift His face to be near you.” This blessing expresses the hope that one should always feel the presence of G-d, for too often we sense that G-d’s face is hidden from us (the Hebrew word yeesah, to lift, is the opposite of G-d being lowered or hidden). Although we hope to always be absorbed in G-d’s presence, sometimes even that experience can distort one’s perception of how to change the world. Too often, people have done dastardly things in the name of G-d. Therefore, the text concludes, with a blessing of a grounded belief in G-d, of shalom, coming from the word shalem, whole. This threefold blessing reminds us that there is no absolute good. Every step forward always contains the possibility of unforeseen problems. May we be blessed with this awareness.