Here is the whole paragraph in context:
"Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, 2 and of instruction about washings,1 the laying on of hands, the resurrection of the dead, and eternal judgment. 3 And this we will do if God permits. 4 For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and shave 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 and then have fallen away, to restore them again to repentance, 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.
The context is that we carry on from being baby Christians to being mature ones, continuing to grow in grace and in the knowledge of God. The alternative is for someone to have a smattering of Christianity and then falling away from Christ when problems and persecution come along. It speaks more of a general rejection of Christ than falling off the holiness wagon. We are all sinners need our Saviour, and are susceptible to temptation, but the promise is that if we confess our sin God is faithful and just to forgive us our sin and cleanse us from all unrighteousness (1 John 1:9). Performance Christianity is basically a Gospel of works. Grace based Christianity is dependent on our faith in Christ and the work of the Holy Spirit within us to develop us into the persons God wants us to be.