It refers to works. It doesn't refer to faith as defined by the Bible. It doesn't refer to the faith that is defined for us in Romans 5:1.endures to the end in belief. Like what Paul was talking about in 2 Timothy So, Paul uses the same language here. And Paul is in the bible. Hmmmm. Also have you ever read Blackaby. Review point 3 in his encountering God.
"Therefore being justified (past tense--a one time act) by faith (and nothing else) we have peace with God.
It doesn't matter what you put in there (enduring to the end--faith, baptism, confirmation, penance, confession, keeping the Ten Commandments, keeping the Sacraments, etc.) It doesn't matter. You are still "enduring." Salvation is a one time act. I can point to you the exact date, and even the approximate time when I put my faith in Christ and was saved. There is no such process of enduring. That is what makes it a false message of works. It becomes a process. It is not a process. It is a one time act of "believe and thou shalt be saved;" Call upon the name of the Lord and thou shalt be saved;" Believe in thine heart...and thou shalt be saved." Over and over again the Bible has the same message: Believe and be saved. It is a one time act. There is no process of enduring. That is what makes it a gospel of works--a false gospel.