"Grace and peace" is Paul's characteristing greetings in all his thirteen letters (with "mecry' interrupting the expression only in 1 & 2 Timothy; see Paul's Greetings).
Grace (charis) is the fountain of God's goodness that makes life with Him, and redemption in all its conceptionable shades and dimensions, possible. Peace (eirene) is that which we experience when grace is the ecosystem in which we live our life. Grace is the solid foundations on which life is lived as it should be lived, and peace the accompanying proof of a life so lived.
And always Paul wishes of it for the recipients of his letters that this grace and peace come from "God our Father and the Lord Jesus Christ." God the Father is the source of all good grace but it is appropriated and understood fully only through the agency of Jesus the Christ.
It has often been suggested by commentators that Paul found the pair that makes up the expression to congenial because grace, charis in Greek sounds like charein, 'greetings,' that is customary of ancient letter writing. Peace, eirene, on the other hand, is typically Jewish, being the Greek word for shalom. In the pair, then, Paul has found a greeting that is equally at home with the Greeks and Jews to whom he preached and wrote. That it went well with both Greek and Jews is a fact, but that the explanation why Paul is so fond of it remains hypothetical. But that it should should surprize no one for it reflects so crisply what lies at the center of Paul's heart; his mission to the Gentiles and the reconciliation of Jews and Gentiles in God's new humanity. The theological richness of the expression (see para.2 above) is so patently apparent that, however, Paul came upon it, anyone who follows after Paul's thoughts about what Jesus has done for us on the cross would immediately be drawn to its power and appositeness as a greeting.
©ALBERITH
190820lch