The forensic nature of justification is that sinners are declared righteous before God. This is a legal act, a verdict handed down by the courts of heaven. Whereas the sinner has nothing in which to boast—no inherent righteousness, nothing to offer, nothing that will please God (cf. Rom. 3:10-18; Isa. 64:6, etc.)—God pardons the sinner, thus treating them as though they are righteous, even though they are unrighteous. In truth, God cannot and will not declare a person righteous by their own merits because it would be a supreme act of injustice! As we’ve seen, apart from God, humans are terrible law-breakers, unregenerate wretches, sons of disobedience, spiritually dead. No human judge would let a mass murderer go free simply because he paid his taxes on time! In the same way, God will not overlook our trespasses and sins on the basis of our religious activities or our good deeds. He declares, “by the works of the Law no flesh will be justified in His sight” (Rom. 3:20). Rather, justification is “a gift by His grace through the redemption which is in Christ Jesus” (v. 24). Jesus tells the parable of two men, a Pharisee and a tax-collector, who come to worship God in the temple.
The Pharisee boasts about his ability to keep God’s Law and accomplish a righteousness on his own. But the tax-collector, ashamed of his sin, has all he can do to beg the Lord, “Be merciful to me, the sinner!” Jesus declares, “I tell you, this man went down to his house justified rather than the other” (Luke 18:13-14). While the Lord sits as judge, exercising His decrees, there is a part to be played for those who would be justified. The key element in salvation and justification is faith. According to Hebrews 11:1, faith is “the assurance of things hoped for, the conviction of things not seen.” Paul makes note of the faith of Abraham, “being fully assured that what [God] had promised, He was able also to perform” (Rom. 4:21). It’s not what we call “blind faith,” rather, it is confident belief in the promises of God, and in His ability to keep them. And the Bible says that faith is the active agent at work; it is the key that opens the lock. We are justified by faith in Jesus Christ (Rom. 3:28; 5:1; Gal. 3:11, 24), and not by our own efforts to justify ourselves. Even as far back as Genesis 15:6, we see Abraham who “believed God, and it was credited to him as righteousness.” Luther writes: “Wherefore it ought to be the first concern of every Christian to lay aside confidence in works and increasingly to strengthen faith alone and through faith to grow in the knowledge, not of works, but of Christ Jesus, who suffered and rose for him.”8 Sinners are not saved by works, rather, “by grace [we] have been saved through faith” (Eph. 2:8). And God, who is Himself just, is “the justifier of the one who has faith in Jesus” (Rom. 3:26).
Adapted from Why We're Protestant by Nate Pickowicz