Paul is praying God’s blessings on those who will walk by this rule which is that they would walk the right path to real salvation which is by faith apart from works. This blessing stands in total opposition to the curse he spoke against those who would pervert the Gospel by adding works to the completed work of Jesus Christ and salvation by grace through faith alone, in Christ alone. This blessing is for true believers in the church and the saved Jews (“Israel of God”). Note the distinction between UPON them and UPON the Israel of God. He uses this term as a last blow against the Judaizer’s who say you need to do works to be saved. The church was never identified with Israel until AD 160 and even then they did not use this term “Israel of God” to speak of the church. Have you trusted in Christ alone, by faith alone in His finished work on the cross (John 19:30)? If not do it today, works will not save you.
Galatians 6:16 And those who will walk by this rule, peace and mercy be upon them, and upon the Israel of God.