In Peaces

One who takes leave from his friend should not say “go in peace” (lech BE-shalom), but “Go to peace” (lech LE-shalom). Jethro told Moses, “Go to peace” – Moses went and succeeded in his mission. David told his son Absalom, “Go in peace” – Absalom went and was hanged. When taking leave of the deceased, however, one should say “Go in peace” The Talmud, Berachot 64a

Why do we use one for the dead and one of the living? For those still living we say” go to peace” the implication being that it will not be easy, that while alive we must always be wary and actively seek peace with the understanding that the way may not always be clear and we will often fail. While in death the physical hardships of life are over and while the soul can continue to grow, its path is not encumbered by material hardships, therefore “go in peace” your physical labor is done, now go peacefully on your way.