We talked before about justification (by faith alone in Christ alone) and new birth. We are justified in God's sight – declared righteous by Him – when we do not work, but believe (Romans 4:5). We have life through His (Christ's) name when we believe (John 20:31). Both are true, but they aren't the same.
There's a temptation when we talk about this sort of thing to err in one of two directions: either we confound two distinct things and blur them together in our minds, or we put them in opposition to one another, and try to force ourselves to choose between them. The proper path is to recognize that we need both, but to understand at the same time that they're not the same thing.
So we understand that being justified in God's sight – being declared righteous by Him – is our guarantee against damnation. God cannot condemn the one He has already declared is righteous. So there's a sense where our eternal destiny is determined by whether we work, or whether we simply believe without works.
At exactly the same time, we understand that we need not only God's judicial acquittal (so that we cannot be condemned in His sight), but we need to be changed. We have an ontological need as well as forensic need. It's not merely that we need to be acquitted, we need to be changed too. We recognize that we aren't what we need to be, and we recognize too that flesh and blood cannot inherit the kingdom of God (1 Corinthians 15:50). We need an entirely new life to see it (John 3:3).
It's important that we don't confuse what Scripture says about these two things. We can search the Scriptures all we like, but we cannot find a single test in Scripture to tell whether we have been justified in God's sight. We can find Scriptural support for the idea that new life in Christ has produces results (1 John 3:9, 14, 24), but I cannot find a "test" of whether we are justified by Him.
As far as I can tell, whenever someone says, "God be merciful to me a sinner," God does exactly that. That self-confessed sinner goes home justified (Luke 18:13–14). This is the foundation of our assurance before Him. We can be confident before God, because we know that He is the God who justifies the ungodly (Romans 4:5). We are confident that He has heard and He has acted when we say, "God have compassion on me, the sinner." We have nothing to fear when we have told Him the truth and stopped calling Him a liar.
But at the same time, we check ourselves against what He says about the life He has given us. Are we living that life? Is that something we have received, but are content to leave in the package, so to speak? We are called not merely to have eternal life, but to "lay hold" on it (1 Timothy 6:12).
And this brings us to an entirely different view of the Christian path. On the one hand, we must be content to call out, "God be merciful to me a sinner" and be confident that He has done exactly that. On the other, we recognize that eternal life requires feeding, as all life does. No living thing, except God Himself, can just go on without feeding. The eternal life we receive from God requires feeding too, which is really what John 6:35–58 is all about. We need not only to have eaten (John 6:53), but also to eat (John 6:56). There is, indeed a one-time eating, but there is also an ongoing feeding. We need both.
Again – we can't stress this enough – being righteous in God's sight has nothing to do with how well live after that. Having once been declared righteous, God no longer counts any sins against us (Romans 4:6–8). That's true regardless how we live from that point on.
Walking in newness of life isn't a result of fear of judicial retribution. We don't walk in newness of life because we're making atonement for our sins, nor because we're trying to acquire merit to buy our place in Heaven. Walking in newness of life is a result of Christ in us. We yearn to walk newly (I really don't think that's a correct use of the word) because He has worked something new in us (Philippians 2:13). And this isn't merely a "New Testament truth," it's taught in the Old Testament too: fallen men and women need a new heart (Deuteronomy 29:1–4).
So my exhortation to us – and I really do mean "us" here, I need to hear this as much as anyone does – is, don't let's lose sight of either truth. On the one hand, we are justified in God's sight without works when we believe Him. At exactly the same time, God works in us to produce something new: and it starts with His giving us new life. We can't work our way into new life, it's impossible to earn eternal life. But the eternal life He has given us freely grows and develops and matures into something very different than what we are by nature as Adam's children.
We need to hold on to both these truths.