Why should he do that after saying there is no Jew or Gentile church but we are all one in Christ?
Saul said that to Jewish Christians who were concerned with their standing in the Abrahamic Covenant and the Mosaic Covenant having been born-again of the Holy Spirit.
The whole letter is written to Jewish Christians in the Galatian region. Those fellowships were founded by Jewish Christians who returned from Pentecost and returned to their synagogues with Jesus on their lips.
Speaking to Jewish Christians:
2 This only would I learn of you,
Received ye the Spirit by the works of the law, or by the hearing of faith?
Gal. 3:1–2.
Speaking to Jewish Christians:
6 Even as
Abraham believed God, and it was accounted to him for righteousness. 7 Know ye therefore that they which are of faith, the same are
the children of Abraham.
Gal. 3:5–7.
Speaking to Jewish Christians:
10 For as many as are of the works
of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the
book of the law to do them.
Gal. 3:9–10.
Speaking to Jewish Christians:
16 Now to
Abraham and his seed were the promises made.
Gal. 3:15–16.
Speaking to Jewish Christians:
19 Wherefore then serveth
the law? It was added because of transgressions,
Gal. 3:19.
Speaking to Jewish Christians:
23 But before faith came,
we [Jews] were
kept under the law, shut up unto the faith which should afterwards be revealed.
24 Wherefore
the law was
our [Jews] schoolmaster to bring
us [Jews] unto Christ, that
we [Jews] might be justified by faith.
25 But after that faith is come,
we [Jews] are no longer under a schoolmaster.
26 For
ye [Jews] are
all [Jews] the children of God by faith in Christ Jesus.
27 For as many of
you [Jews] as have been baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for
ye [Jews] are
all [Jews] one in Christ Jesus.
29 And if
ye [Jews] be Christ’s, then are
ye [Jews] Abraham’s seed, and
heirs according to the promise.
Gal. 3:23–29.
The ONLY PEOPLE that are heirs to the Abrahamic Covenant are JEWS.
Gentiles were not part of the Covenant when God made it and it is IMPOSSIBLE to add Gentiles into a closed Covenant after God made it. It is everlasting in the form God deemed it with Abraham. All attempts to add hard-core, idol-worshiping, uncircumcised, non-covenant Gentiles to the Abrahamic Covenant violates the Word of God in Covenant and is a violation of the God who made the Covenant.
And all TRUE CHRISTIANS should not be a party to such attacks on God and His Word.
Those that do so are FAKES!