Hebrews 6 is difficult to interpret and many good bible scholars come to quite different conclusions about the details, but nearly all agree that there is no basis in this chapter for denying the biblical doctrine of eternal security. The book was written to Hebrews, who had a difficult time turning from their old Judaism performance-based faith. The lesson is to accept that Jesus paid for our sins FOR ALL TIME and move on. We don't need to fret about the possibility of God turning His back on us if our faith falters, since He remains always faithful.