And as many as walk according to this rule. "May they enjoy all prosperity and happiness!" This is not merely a prayer in their behalf, but a token of approbation. His meaning therefore is, that those who teach this doctrine are worthy of all esteem and regard, and those who reject it do not deserve to be heard. The word rule denotes the regular and habitual course which all godly ministers of the gospel ought to pursue. Architects employ a model in the erection of buildings, to assist them in preserving the proper form and just proportions. Such a model (kanona) does the apostle prescribe to the ministers of the word, who are to build the church "according to the pattern shewn to them." (Hebrews 8:5.) Faithful and upright teachers, and all who allow themselves to conform to this rule, must derive singular encouragement from this passage, in which God, by the mouth of Paul, pronounces on them a blessing. We have no cause to dread the thunders of the Pope, if God promises to us from heaven peace and mercy. The word walk may apply both to a minister and to his people, though it refers chiefly to ministers. The future tense of the verb, (hosoi stoichesousin,) as many as shall walk, is intended to express perseverance. And upon the Israel of God [1] This is an indirect ridicule of the vain boasting of the false apostles, who vaunted of being the descendants of Abraham according to the flesh. There are two classes who bear this name, a pretended Israel, which appears to be so in the sight of men, -- and the Israel of God. Circumcision was a disguise before men, but regeneration is a truth before God. In a word, he gives the appellation of the Israel of God to those whom he formerly denominated the children of Abraham by faith, (Galatians 3:29,) and thus includes all believers, whether Jews or Gentiles, who were united into one church. On the contrary, the name and lineage are the sole boast of Israel according to the flesh; and this led the apostle to argue in the Epistle to the Romans, that "they are not all Israel which are of Israel, neither because they are the seed of Abraham, are they all children." (Romans 9:6, 7.)

Footnotes

1 - Israelitikon gar to alethinon pneumatikon kai Iakob kai Isaak kai 'Abraam tou en akrobustia epi tho pistei merturethentos hupo tou Theou kai eulogethentos kai patros pollon klethentos hemeis esmen, hoi dia toutou staurothentos Christou to Theo prosachthontes. "We, who have been brought to God by this crucified Christ are the true spiritual Israel, and the seed of Judah, and of Jacob, and of Isaac, and of Abraham, whose faith was attested, and who was blessed by God, and called the father of many nations, while he was in circumcision" -- Justin Martyr.

And as many as walk - As many as live, for so the word walk is used in the Scriptures. According to this rule. Greek: "This canon"; see the word explained in the notes at 2-Corinthians 10:13.
Peace be on them - See the note at Romans 15:33.
And upon the Israel of God - The true church of God; all who are his true worshippers; see the note at Romans 2:28-29; Romans 9:6, note.

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 Romans 2:29; Romans 4:12 (note).

And as many as walk according to this rule, peace [be] on them, and mercy, and upon the (n) Israel of God.
(n) Upon the true Israel, whose praise is from God and not from men; (Romans 2:29).

And as many as walk according to this rule,.... Or canon; meaning not the canon of the Scriptures in general, which is the perfect rule, and only standard of faith and practice; according to which we are to walk, believe, and act; but either the doctrine of justification by the righteousness of Christ, the subject of this epistle, the truth the apostle had been explaining, vindicating, and confirming; and which to depart from, is going out of the way of truth; and an abiding by it, is walking in it; and is a good rule and standard, by which to distinguish between truth and error; for whatever is contrary to that article of faith cannot be true: or else the rule delivered in the preceding verse, declaring circumcision and uncircumcision to be of no avail in salvation, but a new creature; and to walk according to this rule, is to renounce all trust in, and dependence upon any outward things; to believe alone in Christ, for righteousness and life; to live by faith upon him, and to walk in newness of life, under the influences of his Spirit and grace:
peace be on them, and mercy. This is the apostle's godly wish, unfeigned desire, and hearty prayer for all such persons, be they who they will; Jews or Gentiles, circumcised or uncircumcised: by peace he means, a view of their peace with God, made by the blood of Christ; peace in their own consciences, which passes all understanding, and arises from a comfortable sense of justification by the righteousness of Christ, of pardon by his blood, and atonement by his sacrifice; and which is enjoyed in a way of believing; and also peace with one another, among themselves as brethren, which is a very desirable blessing: in short, it includes all prosperity and happiness, inward and outward, temporal, spiritual, and eternal: and by "mercy", he designs the love and grace of God, to sinful miserable creatures in themselves, which is the spring and fountain of all peace and prosperity; and which is displayed in the covenant of grace, and all the blessings of it; in the mission and incarnation of Christ, and redemption by him; in regeneration, forgiveness of sin, and complete salvation; and intends a fresh discovery, manifestation, and application of the mercy of God to his children; who often stand in need thereof, being distressed with the guilt of sin, or are under desertions or afflictive providences, at which time to have mercy showed them, is exceeding suitable and agreeable: when the apostle wishes these to be "on" them, it signifies that these blessings come from above, as every good gift does; that they descend as a cloud, and rest upon them, and abide with them, refreshing, comforting, and protecting them: he adds,
and upon the Israel of God; which is a further description of the persons, for whom he prays for these blessings; and is not to be understood by way of distinction from them, but as an amplification of their character; and as pointing out the Israel, by way of emphasis, the Israel, or Israelites indeed, the spiritual Israel, as distinct from Israel according to the flesh; see 1-Corinthians 10:18. The "Israel of God", or as the Arabic version reads it, "Israel the propriety of God"; which he has a right unto, and a claim upon; who are chosen by him, Israel his elect; who are redeemed by him, out of every kindred, tongue, people, and nation; who are called by his grace, and are styled Israel his called; who are justified in his Son, and by his righteousness; and for whose sake he is exalted as a Prince and a Saviour, to give them repentance and remission of sin; and who are, or will be saved by him, with an everlasting salvation; and is a name that includes all God's elect, whether Jews or Gentiles: though it may have a particular respect to such of the Israelites, or Jews, God had foreknown and reserved for himself; and who believed in Christ, and walked as new creatures, without confidence in the flesh. The Jews themselves own, that strangers, or proselytes, shall be called by the name of Israel; so they (b) explain Isaiah 44:5, latter part.
(b) Jarchi & Abarbinel in Isaiah. xliv. 5.

A new creation to the image of Christ, as showing faith in him, is the greatest distinction between one man and another, and a blessing is declared on all who walk according to this rule. The blessings are, peace and mercy. Peace with God and our conscience, and all the comforts of this life, as far as they are needful. And mercy, an interest in the free love and favour of God in Christ, the spring and fountain of all other blessings. The written word of God is the rule we are to go by, both in its doctrines and precepts. May his grace ever be with our spirit, to sanctify, quicken, and cheer us, and may we always be ready to maintain the honour of that which is indeed our life. The apostle had in his body the marks of the Lord Jesus, the scars of wounds from persecuting enemies, for his cleaving to Christ, and the doctrine of the gospel. The apostle calls the Galatians his brethren, therein he shows his humility and his tender affection for them; and he takes his leave with a very serious prayer, that they might enjoy the favour of Christ Jesus, both in its effects and in its evidences. We need desire no more to make us happy than the grace of our Lord Jesus Christ. The apostle does not pray that the law of Moses, or the righteousness of works, but that the grace of Christ, might be with them; that it might be in their hearts and with their spirits, quickening, comforting, and strengthening them: to all which he sets his Amen; signifying his desire that so it might be, and his faith that so it would be.

as many--contrasting with the "as many," Galatians 6:12.
rule--literally, a straight rule, to detect crookedness; so a rule of life.
peace--from God (Ephesians 2:14-17; Ephesians 6:23).
mercy-- (Romans 15:9).
Israel of God--not the Israel after the flesh, among whom those teachers wish to enrol you; but the spiritual seed of Abraham by faith (Galatians 3:9, Galatians 3:29; Romans 2:28-29; Philippians 3:3).

And as many as walk according to this rule - Glorying only in the cross of Christ. Being crucified to the world. And, Created anew. Peace and mercy be upon them, and upon the Israel, that is, the Church, of God - Which consists of all those, and those only, of every nation and kindred, who walk by this rule.