1. Jesus died not only for our sins, but for the sins of the whole world (1 John 2:2). Obviously, this doesn't exclude all of the sins that were committed before the time of Christ's death; nor does it exclude all of the sins that have been committed since the time that Christ died. If such were the case, then Christ would have been "the propitiation" for the sins of His contemporaries alone.
Since everyone who lived before Christ had already committed all of their sins and since all of us who have lived since Christ had not yet committed any of our sins, Christ had to die on the Cross of Calvary for all of the sins of all time to truly be "the propitiation" for all sinners—past, present and future.
2. The Apostle Paul teaches that "all [Christians] must appear before the judgement seat of Christ" (2 Corinthians 5:10). The Greek word Paul uses for "judgment seat" is actually "bema seat." The "bema seat" was the platform upon which rulers handed out rewards to the winners of the annual Olympic Games. Thus, the judgement seat of Christ is not a place where Christ judges our fitness for heaven and decides our eternal destiny, since our place in heaven is already prepared (John 14:1-4) and our eternal destiny already determined in Christ (John 3:16). Instead, the judgement seat of Christ is where all Christians will be rewarded for their works (Matthew 16:27; 1 Corinthians 3:10-15; Revelation 22:12), not condemned for their sin (John 5:24; Romans 8:1).
3. In Christ, all of our sins are eternally removed from us (Psalm 103:12), buried where they can no longer be brought up against us (Micah 7:19), and forgotten by God (Isaiah 43:25). This includes all of the sins that we have committed, are committing and will commit.
The question is, "If we have already been forgiven for all of our sins—past, present and future—then why do we need to confess our sins to God?" The answer is twofold.
First, Amos teaches us that two cannot walk together unless they are in agreement (Amos 3:3). Anytime we sin, we have a disagreement with God that breaks our fellowship with Him. The only way to restore our fellowship is to acknowledge our sin and agree with God about it. Once we do, we are back in agreement with God, our fellowship is restored and we can once again walk together.
Second, sin short circuits the power of the Holy Spirit in our lives. To be filled with the Spirit means to be controlled by the Spirit (Ephesians 5:18). Whenever we sin we take back control of our lives and grieve the Holy Spirit of God. The Spirit's enabling power ceases to flow in our lives, since we've put ourselves back in the driver's seat and are now living in our own power. Not until we confess our sin and allow the Spirit back under the wheel of our life will the Spirit's enabling power once again enable us to live as God wants us to.
Although we're already saved from all of our sins—past, present and future—we still need to confess our sins to God (1 John 1:9). Only by doing so can we keep ourselves filled with the Holy Spirit and in fellowship with God.
