I have been crucified with Christ

I am going to try something different today! I will try to use the Ignatius Catholic Study Bible (2nd Edition) to help me understand scripture.

But before I come to the main topic of this post I was quite confused by the appearance of the names of both Peter and Cephas in Chapter 2 of Galatians (I have put the RSVCE and Greek side by side in the link). Isn't Peter the same as Cephas? Why did Paul write the letter as if they were two different persons? And does it matter that Paul put the names of the 3 apostles, who were reputed to be pillars (of the early church), in this sequence: James and Cephas and John (verse 2:9), especially if we consider Peter to be the first Pope at the time? 

From the Study Bible:

• Paul's visit was probably the same visit described in Acts 15:1-29 when he presented the case concerning circumcision of Gentile Christians to the Jerusalem Council.
• It was affirmed at the council that "forcible" circumcision for Gentile Christians was wrong.
• Paul frequently called Peter, Cephas (Gal 2:9, 11; 1 Cor 1:12, 9:5, 15:5); Peter (Greek word Petros) and Cephas (Aramaic word Kēphas) both mean "Rock" (see Matthew 16:18).
• James, the Lord's brother (Gal 1:19) was the first bishop of Jerusalem according to tradition. He was not the Lord's blood brother but a near kinsman (CCC 500). He was listed first in verse 2:9 as a way of undercutting the claims of the Judaizers who had a deep respect of him as the spiritual shepherd of the Jerusalem Church at this time (after Peter fled the city, Acts 12:17).
• Paul's rebuke of Peter at Antioch in public (2:14) was necessary precisely because of Peter's authority and influence in the church. Peter's conduct implied the very thing he had denied at the Jerusalem Council, namely, that Gentile Christians must adopt the ritual laws of Judaism (like circumcision) in order to secure their standing in the covenant and obtain salvation.

A quick scan of the Internet came up with a lot of different opinions and debates. Here are a few of the interesting (but clearly less authoritative) ideas:

• In this Catholic forum "Peter and Cephas are two different people in this passage and this is why Paul chose to speak of the Apostle Peter first and then of "Cephas," one of the 70 disciples along with "James" and "John" who were also not apostles but who were among the original 70 disciples."..."The ASB (CE) has the correct translation of the two names for all the verses but I and many others believe that the "study notes" pertaining to these verses are in error."
• From one of the posts of the christianity.stackexchange.com "Maybe Paul calls Peter (Greek) Cephas (Aramaic) because his actions in Gal 2 denote an Old Testament mindset regarding Gentiles?"..."So the way I see it; Paul is using the old school name Cephas because of the old school way of thinking especially after recognizing that reaching out to the gentiles is important and being influential men, they have caused other christians to avoid gentiles too. The effects of v11-14 seem to take away what they did in v6-9"

 Now with this backdrop Paul reaffirms a very important spiritual lesson:
"I have been crucified with Christ; it is no longer I who live, but Christ who lives in me; and the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me. I do not nullify the grace of God; for if justification were through the law, then Christ died to no purpose." (Galatians 2:20-21)
If I (whether I am a Jew or a Gentile) have put faith in the historical fact that Jesus died on the cross for my sin, I also believe that His teaching will guide me through this earthly life. His purpose for me is not to live as I once did but be united with Him (on the cross through baptism - Romans 6:3-6) in this new grace-filled life that lasts till eternity.

"For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God." (1 Corinthians 1:18)