Most Christians don't talk a lot about sanctification, because it seems so divorced from their daily lives. But most Christians are still concerned with what sanctification entails: has Jesus already accomplished what is necessary to make me holy, or do I need to develop and grow into the holiness Jesus has provided me?
According to Hebrews, both aspects of holiness simultaneously take place in the Christian's life - and that's because of the humanity of Jesus. Hebrews 10:12-14 says, "But when this priest had offered for all time one sacrifice for sins, he sat down at the right hand of God, and since that time he waits for his enemies to be made his footstool. For by one sacrifice he has made perfect forever those who are being made holy" (NIV). The NIV phrase "this priest" is a playful way to refer to Jesus so that Hebrews 10:12-14 can talk about the activity of Jesus.
What are the activities in which Jesus is engaged? Jesus offers a sacrifice for sins, sits down at the right hand of God, waits for his enemies to be subjugated to him, and makes perfect those who are being made holy. But did you notice that it's Jesus' humanity that enables him to perform all four activities?
Jesus offers a sacrifice for sins "for all time." How? As a human priest on behalf of others. Jesus then sat down victoriously at the right hand of God. How? By means of his human priestly action in making the once-for-all sacrifice of himself. Jesus currently waits for his enemies to be put under his feet, which means he's waiting for God to vindicate his sacrifice. Again, how? As the human priest who reigns as God from his heavenly throne, but who has also entrusted his vindication to his Father. Finally, Jesus makes "perfect forever those who are being made holy." This Greek sentence more literally says that Jesus "has completed perpetually/continually those who are being sanctified/made holy."
The idea behind this sentence is that Jesus has completely provided for the sanctification or holiness of anyone who needs it, at every moment of his or her life, since Jesus is the one who is in the process of sanctifying or making them holy. But how does Jesus do this? By the "one sacrifice" of himself that he made as our divine-human priest!
Friends, just as Jesus has accomplished his death, ascension, and heavenly reign by means of his humanity and priesthood, so you can rejoice that every moment of your sanctification is guaranteed by Jesus' human sacrifice, death, and priesthood for you.