"26 For if we go on sinning deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a fearful expectation of judgment, and a fury of fire that will consume the adversaries. 28 Anyone who has set aside the law of Moses dies without mercy on the evidence of two or three witnesses. 29 How much worse punishment, do you think, will be deserved by the one who has trampled underfoot the Son of God, and has profaned the blood of the covenant by which he was sanctified, and has outraged the Spirit of grace?30 For we know him who said, “Vengeance is mine; I will repay.” And again, “The Lord will judge his people.” 31 It is a fearful thing to fall into the hands of the living God."
Hebrews 10:26-31
This warning is given in relation to the possibility of 'going back' and 'falling away' and failing of the grace of God, and is significantly couched in terms of turning away from Christ. And the first evidence of this is lapsing from worship (25). When gathering together in the fellowship of God's people is no longer an attraction, when hearing and studying God's Word no longer appeals, when pleasure in the things of God is so reduced as no longer to be sought after - this is the downward path that leads to spiritual shipwreck. To look upon incarnate goodness and no longer like it, to look on the suffering heart of God as seen in Christ crucified and turn away - this is to have chosen judgment for oneself. There remaineth no more sacrifice for sins when Calvary is spurned. God can do no more; He has nothing more to offer such an one. To refuse all that God has at such infinite cost offered necessarily means to do without Him, and to hand oneself over to His wrath. Well might the Apostle say, 'It is a fearful thing to fall into the hands of the living God' (31).