Peace and mercy to all who follow this rule, even to the Israel of God
Which rule? The rule of the Spirit. Those who regulate their lives by putting complete trust in Christ crucified. They have the peace, the serenity of heart of those who have been justified by faith, having received unjustified mercy.
The Israel of God is a phrase only used by Paul here and it signifies that the blessings of the chosen people are now conferred upon believers; not on those who can trace their racial dependency from Jacob.