Okay, so far we know that our basis is a reliable Bible breathed by God through men of His choosing by which we can now grasp the truth of Christianity. No Bible; no Christianity. Without it, we're just making guesses and offering opinions. We know that God is the central point. He is, above all else, holy, set apart, other than we are. He is One, not plural. He is a Trinity, One God in three persons, coequal, distinct, but not separate. And He has a unique nature. We also know something about Man's nature. He is, first, made in the image of God, and that's good. But, since Adam, Man has also retained the sin nature. We sin because we are sinners by nature. And that's a problem. A big problem. And it was just as much a problem to God as it was to us, since God's nature -- His Holiness and Justice -- demanded payment for, not simple dismissal of, the transgression. The answer to this really big problem is the person and character of Jesus Christ. He is the second person of the Trinity, God the Son. He became actual flesh, lived a sinless life, died on our behalf, and rose again. He paid the price for all of us. He is the only answer to our sin problem, and He is a complete answer. That's what we know so far.
So, the next essential to consider is how, exactly, this solution is applied to our problem. We asked the question way back at the beginning, "What must I do to be saved?" We answered it with the simple requirement of faith, and explained further just in whom that faith must be placed, but the question still hangs there. So, believing in the Lord Jesus Christ is required, but how does that provide salvation? What is the answer to the problem of sin?
The answer is justification. It's a fancy theological term for a simple concept. We need to be made right. However, there are two aspects to this term that need to be applied. First, the debt has to be erased. We have to be made clean. But being clean is only the first step. It is the removal of the dirt. But the demands of righteousness are not merely cleanliness, but righteousness. We have to have sin removed and righteousness applied. And that isn't something that we can accomplish. The idea in Scripture is that justification is by grace through faith in Christ.
First rule: Justification is by faith. Abundantly clear in the pages of Scripture is the simple and quite stunning fact that we are not justified by being good. This is one of those "standalone" areas for Christianity. While every other religion holds that you be good and then you go to heaven, Christianity alone holds that you are justified by faith. This was the Old Testament principle. It is the New Testament principle. It is the absolute hinge pin of Christianity. It was stated way back in Abraham's day when it says, "Then he (Abraham) believed in the LORD; and He reckoned it to him as righteousness" (Gen 15:6). There it is in plain language. "Believe" = "righteousness". Note how that righteousness is received: "reckoned". That's the concept. So, "by grace you have been saved through faith; and that not of yourselves, it is the gift of God; not as a result of works, so that no one may boast" (Eph 2:8-9). That's the principle. By faith; not of works.
Second rule: Justification is by grace. The biblical definition of "grace" is somewhat unique to Christianity. While the idea is "favor", it includes a descriptive that is not the usual. Biblical grace refers to unmerited favor. "If it is by grace, it is no longer on the basis of works, otherwise grace is no longer grace" (Rom 11:6). Salvation by grace -- favor apart from personal merit -- is essential.
And, of course, as already indicated, that grace comes from Christ on the basis of faith in Christ. In no sense is this justification obtained by our own efforts, on our own merits, or based on anything other than Christ.
There is in all of this talk about justification a concept of singular importance. It is called "imputation". The idea is found there in the reference to Abraham in Genesis. Righteousness wasn't earned; it was "reckoned" on the basis of faith. So, God "made Him (Christ) who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him" (2 Cor 5:21). That's the idea. In Christianity, our sin was imputed to Christ on the cross, leaving our slate clean, and, in return, His righteousness was imputed to us on the basis of faith, leaving us righteous.
The formula is complete. The conditions are met. The answer is there. What must I do to be saved? Believe on the Lord Jesus Christ. How does that save? It applies my sin to Christ and applies His righteousness to me. All of this -- justification -- is accomplished not on the basis of works, not on the basis of merit, and not on anything in me. That is justification by grace through faith in Christ. It is unique to Christianity and absolutely essential, a key structure necessary for Christianity to stand.