"...centering on Abraham's faith in Genesis 15:6: "Abraham believed God, and it was reckoned to him as righteousness." Catholics agree with this Scripture, but the same words ("it was reckoned to him as righteousness") are applied to another person in the Old Testament besides Abraham, and the "justification" was there attributed to actions and zealousness, not faith alone.
The phrase used in Psalm 106:31 is the same (in both the Hebrew Masoretic text and the Greek Septuagint) as is used in Genesis 15:6. In Psalm 106:30, 31 we read, "Then stood up Phinehas, and executed judgment: and so the plague was stayed. And that was counted unto him for righteousness unto all generations for evermore" (KJV).
Evangelicals say his faith justified him, like his father Abraham-but the Psalmist must not have understood the faith alone doctrine, for he attributes the imputation of righteousness to Phinehas' zealousness."
The background of this event is recorded in Numbers 25. In it, some of the Israelites were committing fornication with the woman of Moab. Consequently, God was provoked to anger and He cast a plague over Israel. Then, Phinehas took a spear and drove it through a couple in the act of fornication, which killed them both. He obtained mercy from God, terminated the plague, and was regarded as being a righteous man due to his desire for righteousness. His deed would be blessed and remembered in every future generation. Verse thirty-one simply means that God was pleased with this man's decision. The reality of his faith was demonstrated before other men. This is a testimonial of faithfulness, not salvation. Notice how other Bible translations render this verse:
"Because of this, Phinehas was considered righteous forever, throughout every generation." (Psalm 106:31, God's Word Translation)
"Phinehas did what was right, and it will be remembered from now on." (Psalm 106:31, Everyday Bible)
"This was counted for him as a righteous deed for all generations to come." (Psalm 106:31, New American Bible Revised Edition)
"for this he is the example of uprightness, from age to age for ever." (Psalm 106:31, New Jerusalem Bible)
Following is the New English Translation commentary:
Following is another excerpt from the New English Translation on Genesis 15:6:
"tn The noun צְדָקָה (tsedaqah, “righteousness”) occurs with the Niphal of the same verb in Ps 106:31. Alluding to the events recorded in Numbers 25, the psalmist notes that Phinehas’ actions were “credited to him as righteousness for endless generations to come.” Phinehas acted in opposition to idolatry. So he was righteous in motive, his actions were righteous in character, and after he acted he was accorded righteous standing before God. Further the Lord rewarded Phinehas with an unconditional, eternal covenant (Num 25:12-13) as he rewards Abram with a covenant. From that contextual fact, the צְדָקָה (tsedaqah) “righteousness”) may be viewed by some as focusing on the rewardability of the behavior more than the righteous standing before God, though the two notions are related. (See R. B. Chisholm, “Evidence from Genesis,” A Case for Premillennialism, 40.) In Phoenician and Old Aramaic inscriptions cognate nouns may be glossed as “correct, justifiable conduct” and may carry this same semantic nuance (DNWSI 2:962). HALOT seems to focus on the motive and character of righteous actions when it lists “loyalty to the community” among its glosses for צְדָקָה (HALOT, 1006). The translation takes the righteous standing to be central, though it coincides with righteous or loyal motives, righteous conduct, and being viewed as worthy of reward."
Observations from the Jamieson-Fausset-Brown Bible Commentary:
Although people have tried connecting Psalm 106:30-31 with Genesis 15:6 (meaning to equate the phrase "counted for righteousness" in both texts as having the same meaning), the similarity in sentence structure is irrelevant because the context of Numbers 25 and Psalm 106:30-31 is not about how one gets right with God. The passage in Genesis 15 is not the moment of Abraham's justification, but rather is the Lord's promise of salvation to him and posterity through faith. The text of Genesis 15:6 is foretelling the foundational message of salvation as prescribed by the gospel. That is why the Apostle Paul refers to this text from Genesis in his arguments about justification in Romans and Galatians. It is not as if driving spears into sinners is a requirement for salvation.
God will certainly reward Christians for their faithfulness to Him, but we are not saved by works of righteousness (Titus 3:5-7). We are saved because God is merciful, and He saved us in spite of our unrighteousness (Deuteronomy 9:3-6; Ephesians 2:4-9). The gospel requires that one must believe in order to receive justification (John 20:31; Acts 16:29-32; Galatians 3:4-9; 2 Timothy 3:15; Revelation 21:6; 22:17). The gospel in Scripture is defined as the death, burial, and resurrection of Christ (1 Corinthians 15:1-8). That is the power of God to all who believe (Romans 1:16). The just shall live by faith (Habakkuk 2:4; Romans 1:17). This righteous act of Phineas has nothing to do with him meriting his own salvation. The man was already saved. God simply deemed this man's work to be righteous, and assured that the priesthood would not depart from his line.