What does "pax vobiscum" mean?

In my Altar Boy days in the Catholic Church back in the 50s when the Mass was still said in Latin, the phrase Pax vobiscum ( Peace be with you) appeared a few times in the liturgy and the expected response was "Et cum Spiritu tuo" ( And the Spirit be with you as well.)

I have been signing more of my letters and posts these days, "Pax vobiscum" and in English, "Peace be with you."

Nothing real can be threatened. (Referring to the non dual Oneness.)

Nothing unreal exists. (Referring to the impermanent forms of the world of the ego.)

Herein lies the peace of God.