Understanding the Eternal Gospel in a Space-Time World
People are created as finite, limited creatures with limited knowledge. God is infinite, eternal, and all-knowing. We often divide time into 3 categories: past, present, and future. The past generally becomes less familiar to us as a greater amount of time passes, although certain events will tend to stand out more than others. The future is wholly unknown to us, although often we are able to make reasonable guesses about many routine events.
But, to God, there is no fading away of the past memories or uncertainty about future events. All events are to God clearer than the clearest experience we have of the present. Often, we tend to forget our sins of the past as our memory fades, and we become less troubled by them. That is not the case with God. He sees our sins of the past (and future) just as clearly as the sins we commit in the present. When Christ took on our sins on the cross, they were as sickening and repugnant as they were when they were being committed. God, the judge dealt with them as a righteous and holy God should, and Christ bore the consequences of our sin. This means that our sin has been removed from the entirety of our lives: past, present and future.
It seems easier to comprehend the removal of our past sins, but it is more difficult to envision how our future sins were also removed. Someone might say that it would be impossible to sin in the future, then. However, this is a misuse and misunderstanding of the eternal from our past-present-future existence. A similar issue was dealt with by Paul in Romans 6:1 when he said, "What shall we say, then? Shall we go on sinning so that grace may increase? By no means! We died to sin; how can we live in it any longer?"
Another time issue concerns assurance of salvation. In salvation, a sinner is cleansed from his sin. It is given freely, without any work or merit on our part. If our lives ended at the moment of receiving of salvation, nothing more would need to occur. But, because we are space-time creatures that will usually continue on in this life, we need refreshing in the experience of salvation. Without it, there is spiritual death. God has provided refreshing in the preaching of the law and Gospel, in remembrance of baptism, and in receiving body and blood of Christ in the Lord's supper. These experiences allow the continual realization of our state of sinfulness and of the price paid for us on the cross. This is the way the Bible describes the gospel is worked out in a space-time world.
The Reformed church will argue that this means that we must do some works (availing ourselves of the sacraments, and exposing ourselves to the preaching of the gospel) to remain in salvation. They would say that discovering that we are the elect is the only basis of salvation that doesn't require works on our part. We as Lutherans would reply that this is the way that is laid out in the Bible, whether it appears to encourage works-righteousness, or not. However, the Reformed church encourages its members to use experiences from their lives that show God at work as evidences for assurance of salvation. These are much more easily entangled with their own works than a sacrament announcing forgiveness for sin. While there are many who falsely trust in a dead outward observance of the sacraments and church attendance, this is a less troubling error than those who trust in an experience of salvation or upon their Christian lives for assurance of salvation. They do not continually experience the reception of salvation, only the remembrance of it. We are instructed to remember Christ, not our experience of salvation.
Calvinists maintain that since Lutherans do not teach the doctrine of the preservation of the saints, Lutherans will not have any hope of persevering in the faith until death. However, the reason we do not teach it is that we are not to look to our lives (either what we do or what God does in our lives) for assurance of salvation. We look to the cross. Evidences of God's work in us are used only for secondary purposes. The doctrine of preservation of the saints would have us look to our lives for some kind of evidence that we are the elect, and then based upon that conclusion, determine that we cannot fall from grace in the future. While this doctrine is probably better than most modern evangelicals who base their assurance of salvation upon their relationship with Christ instead of either the cross alone or the doctrine of the preservation of the saints alone, the doctrine of the preservation of the saints (sometimes called eternal security) is still incorrect because there needs to be a realization of the demands of the law (including the demand of continuing in the faith to the end) and the dangers of God's judgment to drive the Christian to the cross, where alone is true assurance of salvation. The doctrine of the preservation of the saints removes this realization from a Christian.
To assuage their fear that in the "future" they will depart from the faith and go lost, Calvinists must trade in basing their present assurance only upon the cross and look for evidences that they are part of the elect. It is not a good trade, and unfortunately makes them look away from the cross to their own lives in which it is often very difficult to distinguish between the works of the Holy Spirit and our own works.