Romans 1:16-17b

I am not ashamed of the gospel, because it is the power of God for the salvation of everyone who believes: first for the Jew, then for the Gentile. For in the gospel a righteousness from God is revealed, a righteousness that is by faith from first to last, just as it is written: "The righteous will live by faith."

(v16-17, NIV)

How is this righteousness from faith to faith as NASB puts it? As we read here in NIV it says, by faith from first to last. This righteousness refers to his imputed righteousness on us. In addition, Paul seems to be referring to future saving with regards to the gospel here in verse 16 and 17. This is the power of the gospel to save believers and keep them till the Day of Judgment. This faith to faith or faith from first to last refers to the keeping of faith. When we are saved, we are saved by grace through faith. We meet with faith initially, but God's saving work of his gospel of grace is powerful enough to continue us through increasing faith. You may argue that some fall away, but we know that those who fall away prove to never have been of us. God keeps those he saves, and those he saves he grows their faith. This keeping and strengthening of God in his Gospel is what is being referred to when he says "by faith from first to last".