So, who sets the rules for Christian living?
God. He does this via the Bible (the commands given to us by Jesus and His followers).
You said:
So, the Scripture is not true when it says, "By grace are you saved through faith, it is not of yourself, but it is the gift of God." I don't see anything added to that.
How about Paul? Is he wrong when he said that anyone who tries to live by the Law to be accepted of God brings a curse upon himself?
In most cases, when Paul mentioned the "Law" he was referring to the Law of Moses (the 613 laws as a whole contractually speaking, kind of like a contract in buying a house). The old contract is no more. No more circumcision, Sabbath keeping, dietary laws, animal sacrifices, etc. But this does not mean we are not under "no law", though. Hebrews 7:12 says the Law has changed. So we are under New Covenant Law (i.e. the commands from Jesus and His followers).
In other cases, like with Ephesians 2:8-9 Paul was referring to "Works Alone Salvationism." This is because Paul knew about the heresy at the Jerusalem council that was addressed about how a certain sect of Jews were trying to deceive Christians into thinking they needed to FIRST be circumcised in order to be saved. For if a person thinks they need to FIRST be circumcised to be saved, then God's grace through faith (accepting Jesus as one's Savior or seeking forgiveness with Him) does not mean anything. To be saved by circumcision FIRST would mean a person is ultimately saved by a work (or works). But we know we receive salvation as a gift. If you receive a gift, this is talking about "Initial Salvation." Ephesians 2:1 says, "You
hath he quickened, who were dead in trespasses and sins;" Being quickened is a one time event. Paul is talking about the entrance gate or the WAY to be saved. Paul is saying that we do not first become saved by doing works, but we FIRST become saved by receiving the gift of God's grace (Jesus Christ). But like all good gifts in life, we have to do works of responsibility to maintain them (Which is where verse 10 comes into play). For we are created unto Jesus for good works, and we should (not maybe) walk in them. For James says faith without works is dead (James 2:17).
In other words, Paul and James are fighting two different heresies.
Paul is fighting Law Alone Salvationism or Works Alone Salvationism that does not include God's grace through faith (Note: We are initially and ultimately saved by God's grace), and,
James is fighting against Belief Alone-ism. For even the demons believe and tremble (James 2:19). For James says he will show you his faith by his works (James 2:18). Yet, Protestants define faith as a belief alone and not in the same way as James describes it. A true saving faith is evidence by works of faith, and not sinful works.
You said:
Also, if the Scriptures are not the only authority for salvation and holy living, then what are you adding to it?
I believe in Sola Scriptura or the Bible alone as my sole authority for spiritual matters. So I don't believe we should add anything to it. I am the kind of believer that if it is not in the Bible, we should not do it. This goes for even attending regular churches. We do not see that in the Bible. But we do see fellowship of believers in people's homes, though.
You said:
Did you know that Jesus was Sola Scriptura? All His quotes when He said "it is written", He quoted from Scripture. He never referred to Jewish tradition as authority; in fact He told the Jews that their tradition made the Word of God of none effect.
I created a rather lengthy two part post on a biblical defense for Sola Scriptura here:
A Biblical Defense of Sola Scriptura!
I am not Catholic or Orthodox, etc. I am a Trinitarian, Sola Scriptura non-denominational Christian. I just believe the Bible in what it says; And the Bible teaches we need both Faith in God's grace (Jesus and what He has done for us) + Works of Faith to be saved.
For if works do not play any part in the salvation process whatsoever, then that means that believers can be axe murdering rapists and child abusers until the day they die without any remorse and still make into the glory of Heaven (all because they had a belief on Jesus). But that does not seem right. For is God unrighteous? Surely not.