Apostasy: Fallen from Grace

Galatians 1:
1 Paul, an apostle, (not of men, neither by man, but by Jesus Christ, and God the Father, who raised him from the dead;)
2 And all the brethren which are with me, unto the churches of Galatia:
3 Grace be to you and peace from God the Father, and from our Lord Jesus Christ,
4 Who gave himself for our sins, that he might deliver us from this present evil world, according to the will of God and our Father:
5 To whom be glory for ever and ever. Amen.

Galatians were truely saved churches of God and justified by faith only.

Galatians 3:
11 But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith.
12 And the law is not of faith: but, The man that doeth them shall live in them.
13 Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree:
14 That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.

But, if they do not abide, stand fast in saving faith, then they are fallen from grace.

Galatians 5
1 Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage.
2 Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing.
3 For I testify again to every man that is circumcised, that he is a debtor to do the whole law.
4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.