6:6
“Who have fallen away”. Now what does he mean by “fallen away”? Our immediate reaction is probably to think that it refers to moral sin (eg adultery, thieving etc), but given that none of the preceding text (all five chapters of it) has been concerned with Christian behaviour, but about what we put our faith in, this may not be the case. So it could be that it refers to those who have tasted of the goodness of the gospel, but even then choose to trust in some other means of justification (Jewish sacrificial and religious system, in the case of the Hebrews). This then makes sense of the second part of the verse. The Jewish leaders crucified Christ because of His challenge to the whole Jewish religious system, so those who reject Christ were doing exactly the same thing, though obviously in a metaphorical sense.
Now the question that everyone asks is if someone falls away is this text saying that there is no hope for them? This is the wrong question. The primary aim of the writer is that we do not fall away, that we trust only in Jesus Christ, in His sacrifice, and in His priesthood, and do not go following after anything else. What if we see someone else going down that road? Well pray for them, and if we have opportunity, remind them of the truth, and the seriousness of the matter, just as the writer of the Hebrews is doing here. Hopefully we are not in that position, then let us learn more of the depths of who Christ is, and of His priesthood and sacrifice, as the writer of Hebrews is teaching us.
If all you are interested in is having a debate then these verses are a problem. In reality they are no problem at all, certainly not in terms of practical discipleship.
The once saved always saved thing is useless. I do believe my salvation is absolutely secure because I have confidence in Christ. I also know that what I do with my life matters, and I must seek to live my life according to God’s word, with the help of the Holy Spirit. And what if a close friend or relative once made a profession of faith but has since fallen away in some sense? Are we to think, well because they once made a profession of faith they will go to heaven anyway? This is not the way to think. Instead we should be praying for that person to truly repent and for them to know Christ now and to exhibit the fruit of the gospel now.
6:7
“He who has ears to hear, let him hear” (Mark 4:9) are words that Jesus often said. Moreover, the Father commanded us to listen to Jesus (Luke 9:35). We need to pay attention to the words of the gospel. Jesus also said you will know a tree by its fruit. Mere hearing of the word is never considered enough in the Bible, we need to receive and respond to the word, to be transformed by it. That is what the writer to the Hebrews is saying here.
6:8
The converse is that if we do not produce good fruit, but only thorns and thistles then we are in severe danger. These analogies are common to both the Old and New Testaments. Whatever the minutiae of debates over the security of our salvation, the whole of Scripture is clear that we must take God’s word seriously and to do otherwise is to put ourselves in a precarious position.