{But when I saw} (All' hote eidon). Paul did see and saw
it in time to speak. {That they walked not uprightly} (hoti
orthopodousin). Present active indicative retained in indirect
discourse, "they are not walking straight." Orthopode(935c)
(orthos, straight, pous, foot). Found only here and in later
ecclesiastical writers, though orthopodes bainontes does occur.
{According to the truth of the gospel} (pros t(886e) al(8874)heian tou
euaggeliou). Just as in  2:5 . Paul brought them to face
(pros) that. {I said unto Cephas before them all} (eipon t(9369)
K(8870)h(8369) emprosthen pant(936e)). {Being a Jew} (Ioudaios huparch(936e),
though being a Jew). Condition of first class, assumed as true.
It was not a private quarrel, but a matter of public policy. One
is a bit curious to know what those who consider Peter the first
pope will do with this open rebuke by Paul, who was in no sense
afraid of Peter or of all the rest. {As do the Gentiles}
(ethnik(9373)). Late adverb, here only in N.T. Like Gentiles. {As
do the Jews} (Ioudaik(9373)). Only here in N.T., but in Josephus.
{To live as do the Jews} (Iouda(8b7a)ein). Late verb, only here in
the N.T. From Ioudaios, Jew. Really Paul charges Peter with
trying to compel (conative present, anagkazeis) the Gentiles to
live all like Jews, to Judaize the Gentile Christians, the very
point at issue in the Jerusalem Conference when Peter so loyally
supported Paul. It was a bold thrust that allowed no reply. But
Paul won Peter back and Barnabas also. If II Peter is genuine, as
is still possible, he shows it in  2Pe 3:15 . Paul and Barnabas
remained friends ( Ac 15:39f.  1Co 9:6 ), though they soon
separated over John Mark.