My husband, who is far more insightful than I am, commented once that all the questions essentially boiled down to a couple of basic ideas. Is salvation really a gift? Isn't there something I need to do to add to it? The answer is the same: If our salvation depended on something we could do, we have no hope. It's the same question the apostle Paul dealt with, it was still being asked in Bavinck's time, and it's one we'll be grappling with until Jesus comes again.
Justification is the doctrine on which the church stands or falls. Either we must do something to be saved, or our salvation is purely a gift of grace. If our work, our virtue, our sanctification is primary, then we remain in doubt and uncertainty to our last breath; Christ's unique, all-encompassing, and all sufficient mediatorial office is set aside and God is robbed of his honor. 
For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast. (Ephesians 2:8-9)
We cannot earn our salvation, but because of Christ, we can be assured of our salvation, right down to our dying breath.
 Herman Bavinck, Reformed Dogmatics: Abridged in One Volume, ed. John Bolt (Grand Rapids: Baker, 2011), 563.