Also, consider Acts chapter 15.
In Acts chapter 10, Peter had preached to Cornelius, and the people with him, who were not Jews.And they most likely had never kept any rituals of the Jewish Law and probably never did.
Now while Peter preached to these people, they were saved, without any immediate good works or Law Keeping.
Now, all the way to chapter 15 of Acts, these Gentiles(non Jews)had been saved unless they had turned their back on God.But here in the first verse of Chapter 15, it says that "certain men which came down from Judea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved."
Now, like I said, all this time these Gentiles had been saved, most likely without being circumcised or keeping the Law of Moses.But these people were saying that accept you be circumcised after the manner of Moses, that you could not be saved, which was not true at all.
In Romans Paul points out the fact that God imputed Righteousness to Abraham BEFORE the covenant of circumcision, showing that it had nothing to do with him being saved and having Righteousness.
Now, back in chapter 15 of Acts, you can see that Paul and Barnabas had an argument with these people who were proclaiming this.And later some of the Pharisees said that it was needful for them to be circumcised and keep the Law of Moses, which would be adding something to what Jesus did to save us, His death on the Cross.But there was nothing that had to be added, seeing that these Gentiles had been saved all this time without adding these things.
So the early Church had a big meeting to determine whether this was right or not.Verse 7 says, "And when there had been much disputing, Peter rose up, and said unto them, Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles[non Jews]by my mouth should hear the Word Of God, and believe.And God, who knoweth the hearts, bare them witness, giving them the Holy Ghost, even as He did unto us[the Jews];and put no difference between us and them, purifying their hearts BY FAITH.Now therefore, why tempt ye God to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear?But we believe that through the GRACE of The Lord Jesus Christ, we shall be saved, even as they."
Peter said all these things, and the meeting of the church concluded that these things were not neccasary for salvation, and I believe, not neccasary to maintain salvation either.
So the Church in Jerusalem, where I think this meeting took place, sent a letter to the Gentiles, saying, in my own words, that they did not have to do those things that the people at the beginning of the chapter had said had to be done, thus assuring them that it was not neccasary for salvation, and that they were already saved without these things, by Grace, through what Jesus did by dying for us, and us accepting Him as our Savior.And the letter also just told them things that they were not to do, things that could take away their salvation, which they had by Grace, without good works.
Edit:And like you said, Ghostwriter, the man on the Cross, who was a criminal or something like that, did not have any good works that he could use to get him salvation, as none of us do.But he was saved right there on the Cross, and went to Paradise just like Jesus said he would, even though he did not have any time to do any good works to get him to Heaven.It was purely Grace, as it is with all.