Huh? Sin is very much an issue. Heb. 9:12 tells us that Christ's sacrifice secured our redemption, but redemption is not the same thing as salvation. We participate in and hope for salvation. Our hope in salvation is a guarantee if we are faithful to Christ to the end. But if we lose hope and fail to persevere, we can lose our salvation. Thus, by our own choosing (not by God's doing), salvation is not a certainty.