As the Divine Liturgy is coming to its conclusion, the Priest says, “Let Us Depart in Peace.” Like in so many other things he says in the Liturgy, the priest is speaking to the congregation, not to God. It is a continued part of the dialogue between the priest and the people as they speak antiphonally on the way. The words echo those of St. Simeon the God Receiver who came into the Jerusalem Temple at the very moment the 40 day old Jesus was brought there by His parents. He saw the salvation of God and was ready to depart. So too all who have participated in the Liturgy and received Holy Communion have seen the salvation of God and are ready to depart, not from the world, but into it.
In the book, The Living God (p. 92) we find this explanation:
“Then the priest sends us out into the world, just as Christ sent His apostles: “Let us depart in peace.” We Christians, as communicants, become responsible for radiating the presence of God in the world. Through grace, God grants us the light which shone from the body of our Lord Jesus Christ. Let us ask Him to teach us to transmit this divine Light to mankind and to the whole earth: “You are the light of the world. A city set on a hill cannot be hid. Nor do men light a lamp and put it under a bushel, but on a stand, and it gives light to all in the house” (Matthew 5:14-15).