"The Greek words for "righteous" ("just") and "righteousness" are used a few hundred times in the Bible, so if the Protestant thesis is true, there should be some clear evidence for it. Most of the occurrences uses the terms "righteous" and "righteousness" in passing, so not much can be gleaned from the bulk of the texts. That said, I did not find a single instance where "righteous" or "righteousness" was tied to perfectly keeping the law or commandments. This means that the Protestant definition does not come from the Bible, and rather from traditions of men. Instead, the notion of being righteous, according to Scripture, simply refers to doing good actions (e.g. Mt 6:1; Acts 10:35; Eph 6:1; 1 Th 2:10; 1 Jn 3:7,12) or having an upright quality about your character (e.g. Mt 1:19; Lk 1:6; 1 Tim 1:9; 1 Pt 3:14). Nothing is ever implied about perfect or flawless obedience."
It should be emphasized that the idea of "perfect obedience" encompasses both obedience to God's commandments and reflecting His upright character. This obedience is inextricably connected with good character and conduct. If something is good by its very nature, then that means it reflects the goodness of God. There exists no type of goodness that does not reflect God's character. He requires that His creatures represent or embody His righteousness, which is perfect. Any standard lower than that is sin and falls short of God's glory (Ezekiel 18:4; Romans 3:23; 1 John 3:4). In addition, the following excerpt contains these insightful comments:
"All that He is and all that he does is right and unlike humans, He is righteous in all He says as that is one of His attributes. The Old Testament says that God is righteous. In Psalm 7:11a we read “God is a righteous judge.” The word righteous in the Hebrew is “tsaddiy” which means just, lawful, and correct. The word righteous in the New Testament comes from the Greek word “dikaios” which means observing divine laws or upright, faultless, innocent, and guiltless. These are all descriptive of God Himself and no human has any of these attributes inherent in themselves even though we can do things that are upright and observe the divine laws like the Ten Commandments while not being able to obey them all..."
"In Matthew 3:15, Jesus says He is going to "fulfill all righteousness," which Protestants have long pointed to as proof that Jesus came to perfectly keep the law in our place. But the fact is, the text doesn't say this is about perfectly keeping the Law, especially since the term "fulfill" does not mean "keep perfectly". This ties into another Protestant error, which is assuming the phrase "righteousness of God" refers to Jesus' perfect obedience to the Law. But the problem with that is this is referring to the "righteousness of God the Father," and we know the Father didn't have to keep the law perfectly to have this righteousness (Jn 17:25). Instead, this "righteousness of God" refers principally to God's faithfulness, which is why Scripture contrasts it to our unfaithfulness (Rom 3:3-8). So that approach is clearly a dead-end."
The simple answer to Nick's argument here is that words have meaning and connotations which are dictated by their respective contexts. This commentary expounds rather eloquently on the text of Matthew 13:17:
"Jesus came into the world to identify with men; and to identify with men is to identify with sin. He could not purchase righteousness for mankind if He did not identify with mankind’s sin. Hundreds of years before Christ’s coming, Isaiah had declared that the Messiah “was numbered with the transgressors; yet He Himself bore the sin of many, and interceded for the transgressors” (Isa. 53:12). Jesus’ baptism also represented the willing identification of the sinless Son of God with the sinful people He came to save. That was the first act of His ministry, the first step in the redemptive plan that He came to fulfill. He who had no sin took His place among those who had no righteousness. He who was without sin submitted to a baptism for sinners. In this act the Savior of the world took His place among the sinners of the world."
"Paul is saying the righteousness that the law gives is a non-saving righteousness (it only gives one earthly blessings like long life, wealth, big family, etc). The righteousness that does save and bring about forgiveness of sins comes from God through faith. This is why Paul can say: "I do not nullify the grace of God, for if righteousness came through the law, then Christ died for no purpose" and "not having a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God" (Gal 2:21; Phil 3:9; cf Rom 10:5-6). Paul is saying there are two types of righteousness - a saving righteousness and a non-saving righteousness - where as Protestants mistakenly think there is only one type of righteousness. Thus, the door is slammed again in attempting to identify (saving) "righteousness" with perfect/sinless commandment keeping."
We can agree with Nick that the Mosaic system was never a means of salvation. We can even agree with him that it is impossible for us in our fallen condition to obey it perfectly. However, that is precisely why the Law condemns us. We are all sinners in need of a Savior. The Apostle Paul spoke of the true righteousness that originates in Christ in contrast with a law righteousness that is not pleasing in God's sight due to it falling short and resulting in fleshly boasting.
It is the righteousness of Christ alone by which we are justified before God. It is only by means of being accepted in Christ that any works that we perform are acceptable to God. A person must first be recognized as a member of God's kingdom. Only then can his works be of any value.