"First, Piper has not been consistent with the parallelism of the passage: 4:6 Blessing to whom God credits righteousness apart from works, 4:7 Blessed are those whose iniquities are forgiven, and 4:8 Blessed is he whom the Lord will not reckon his sin. Notice that the parallel is not of “iniquities” and “sin” corresponding to “apart from works,” as Piper hurriedly assumed, but rather the “crediting of righteousness” corresponds to “iniquities forgiven” and “not crediting sin.” In other words, Paul is saying that to “credit righteousness” is synonymous with “not crediting sin. Thus, there is no actual correspondence between “apart from works” and “sinner” here."
First of all, it is somewhat foolish to try to use one passage of Scripture to refute a doctrine so profoundly and clearly enforced by that same text. Romans 4:6 is explicitly speaking of those, "to whom God counts righteousness apart from works." That is the direct quotation of that verse. There is no way that those things can be separated.
It is true that the crediting of Christ's righteousness corresponds to our iniquities being forgiven. That is double imputation. Our sins are credited to Christ and His righteousness is credited to us. The Reformation Study Bible has this footnote:
"4:6–8 That Paul’s exegesis of Gen. 15:6 is correct is confirmed by an appeal to David’s words in Ps. 32:1, 2. Blessedness (fellowship with God together with all its accompaniments, and salvation) is not earned, but is the effect of the gift of forgiveness. It is by Christ’s work, not ours, that we are justified. Any merit of our own, even the good that redeemed people do by the tower of the Holy Spirit, is excluded."
The key to interpreting the passage is verse 2, which says, "For if Abraham was justified by works, he has something to boast about, but not before God.” Paul is making a case that Abraham and others are not justified by works because then we could boast before God. Verse 4 further supports this idea with the simple point that if someone earns wages, then it is not a gift. Verse 5 then says that God justifies the ungodly and counts them as righteous by faith. The text is crystal clear in rebuffing the Roman Catholic view of meritorious works in justification. King David is quoted in here as an example of being justified in spite of his transgressions against God.
Justification by faith alone includes forgiveness and the imputation of Christ’s righteousness. It is an exchange of our sinfulness onto Christ and His righteousness onto us. The lines do parallel one another by emphasizing the different sides of justification. Verse 6 says that King David is credited or counted as righteous apart from works. 7-8 is emphasizing our pardon from sin. The overall point from these parallel phrases is that we are not justified by works. They do not merit our salvation.
"Second, consider that Piper shows there is just as much of a parallel between 4:5 and 4:6 as there is between 4:6 and 3:28. Here Piper shows that “justified by faith apart from works of the law” (3:28) is to be understood synonymously with “credits righteousness apart from works” (4:6). Thus, the “ungodly” is one who is “apart from works of the law.” Realizing this, it is even less reasonable to say “apart from works of the law” is a synonym for “sinner” in general (for example, being uncircumcised does not make one a sinner in general)."
This paragraph does not follow at all. We can agree with the first part of what is being said, "“justified by faith apart from works of the Law” (3:28) is to be understood synonymously with “credits righteousness apart from works” (4:6). That part of the argument makes perfect sense. However, Nick follows that with, "Thus, the “ungodly” is one who is “apart from works of the Law.” In light of this, it is even less reasonable to say “apart from works of the Law” is a synonym for “sinner” in general (for example, being uncircumcised does not make one a sinner in general)." It is difficult to see where Catholic Nick gets this conclusion from. It is not connected to nor logically flows from the first part of that paragraph.
"The only fitting explanation is that “ungodly” is a slang (or even pejorative) way of speaking of a Gentile, who is by definition someone who lacks works of the law. Note this parallel found in Galatians 2:15-16. And not only is this the only consistent way to interpret that parallel, it's the only way to make sense of Paul's earlier statements regarding Abraham."
This does not seem to fit at all as a logical flow. Moreover, how somebody can draw a distinction between an ungodly person and a sinner is far beyond me. If the ungodly are without good works (which means that they are lawless), then that means they are a sinner in need of having faith accounted to them as righteousness. Abraham needed the same.
Nick ignores the language of sin and the need for the covering of it in the passage itself. Also, formulating a sharp distinction between having the Law and actually being a sinner is not legitimate because without the Law, a person cannot be certain as to what what is sinful verses what is not. Nick seems to be implying that Gentiles are not actually sinners; the Apostle Paul is simply occupying the term as a word without any meaning other than "someone who does not have the Law of Moses." Paul's use of the language of sin and iniquity in Romans 4 is therefore rendered superfluous.
The very reason one might be able to boast before God is precisely because of the absence of sin and the keeping of the Law, as opposed to Gentiles who do not have the Law and sin. In summary, Catholic Nick has turned Romans 4:5-8 right on its head.