Youare ignoring the context. "Therefore" refers back to what is said before the therefore. What is the "it" that "is of faith, that it might be according to grace"?
Look at the previous few verses to find out.
"For the promise
that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith. For if they which are of the law be heirs, faith is made void, and the promise made of none effect. Because the law worketh wrath: for where there is no law, there is no transgression. Therefore
IT is of faith that it might be according to grace, so that the promise might be [
d]sure to all the seed, not only to those who are of the law, but also
to those who are of the faith of Abraham, who is the father of us all 17 (
as it is written, “I have made you a father of many nations”)
IT is the thing promised to Abraham,
that he would be the father of many nations and heir of the world. It is neither atonement, nor Justification, nor salvation, in this context. The text you are citing here has nothing to do with the topic R C Sproul was discoursing on.
Being redeeemeed, being justrified and being saved are three different things. They are spelt different. They look different. The mean different things.