Circumcision and the Law

Galatians 5:2-3 NASB
2 Behold I, Paul, say to you that if you receive circumcision, Christ will be of no benefit to you.
3 And I testify again to every man who receives circumcision, that he is under obligation to keep the whole Law.

Who is speaking and testifying?
To whom is he speaking and testifying?
What two things are they told about receiving circumcision?
What has Paul previously mentioned about circumcision in Galatians? (Skim through chapter 2.)
Between what two groups do you see a tension in Galatians, chapter 2?
Is there evidence that the gospel was intended by God for just one of these groups?
Which group seems to think that might have been the case?
Of what does Paul remind this group in Galatians 5:2-3?
Paul dealt with this question of circumcision many times in his ministry among the Gentiles. Read what he wrote to the Romans, Philippians, and Colossians in these verses:
Romans 2:28-29, Philippians 3:1-11, and Colossians 2:9-12.
Do you see a parallel between the circumcision by God or man--and the birth according to the flesh or through the promise?