Hebrews 6

As a Calvinist, this passage always gives me pause:

Hebrews 6:4-8
(4) For it is impossible to restore again to repentance those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit,
(5) and have tasted the goodness of the word of God and the powers of the age to come,
(6) if they then fall away, since they are crucifying once again the Son of God to their own harm and holding him up to contempt.
(7) For land that has drunk the rain that often falls on it, and produces a crop useful to those for whose sake it is cultivated, receives a blessing from God.
(8) But if it bears thorns and thistles, it is worthless and near to being cursed, and its end is to be burned.

What do we do with this? Is it possible to lose our salvation? Is salvation a matter of works? How can we possibly hold up to this?

I would say that a casual reading would suggest that we could lose our salvation. However, I think that it stands in odds with a passage like Ephesians 1:13-14. How can we be sealed by the Holy Spirit and yet live in constant fear of messing up? The rest of the chapter helps to clear this up:

Hebrews 6:17-20
(17) So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath,
(18) so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us.
(19) We have this as a sure and steadfast anchor of the soul, a hope that enters into the inner place behind the curtain,
(20) where Jesus has gone as a forerunner on our behalf, having become a high priest forever after the order of Melchizedek.

Jesus is our righteousness! He is the one who has lived perfectly and we do not have to fear judgment for our sins. This does not give us a license for wanton sin, but it does mean that we do not have to worry about whether or not we measure up in the scales of God's justice. We can't possibly measure up, but Christ can. Isn't this is a wonderful promise?

If you are on the treadmill of chasing after God's pleasure through your works I encourage you to look to Christ for our righteousness. Of course, this does show that there is value in our works:

Hebrews 6:10-12
(10) For God is not so unjust as to overlook your work and the love that you showed for his sake in serving the saints, as you still do.
(11) And we desire each one of you to show the same earnestness to have the full assurance of hope until the end,
(12) so that you may not be sluggish, but imitators of those who through faith and patience inherit the promises.

However, our works don't save us.

So what to do with this passage that suggests that we can fall away forever? I would maintain that those who fall away like that were never sealed by the Holy Spirit as described in Ephesians 1:13-14. That seems to be the common Calvinistic interpretation.

What do you think?