Adam Clarke on Galatians 6:16

As many as walk according to this rule - Τῳ κανονι τουτῳ· This canon; viz. what is laid down in the preceding verses, that redemption is through the sacrifice of Christ; that circumcision and uncircumcision are equally unavailable; and that none can be saved without being created anew. This is the grand canon or rule in Christianity.

Peace be on them - Those who act from this conviction will have the peace and mercy of God; for it is in this way that mercy is communicated and peace obtained.

The Israel of God - The true Christians, called here the Israel of God, to distinguish them from Israel according to the flesh. See the notes on Rom 2:29; Rom 4:12 (note).