The message of Hebrews is about the greatness of Jesus Christ and how he fulfilled all of God's saving promises through his coming (v. 1:1-3) life (v. 4:15), death and resurrection (v. 9:14; 10:14), and glorious ascension (v. 12:2) as the Son of God.
Chapter 6 is the most important chapter regarding the warning passages in Hebrews. It is in this chapter we learn the reason why the warning passages were written:
"And we desire each one of you to show the same earnestness to have the full assurance of hope until the end, so that you may not be sluggish, but imitators of those who through faith and patience inherit the promises." (Hebrews 6:11-12 ESV)
Why does the Hebrews author write warning passages? To ensure the audience would show the biblical vigor to have the full assurance of the gospel in their hearts and live in obedience to that fundamental NT reality.
These were the problems that lead the author of Hebrews to write warning passages:
"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, and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment." (Hebrews 6:1-2 ESV)
I agree with Schreiner who says, "The importance of obedience and perseverance is woven throughout the letter to the Hebrews, for the readers were tempted to relapse to Jewish practices to avoid discrimination and persecution" (p. 595). The warning passages do not suggest that the readers [who were reverting back to Judaism instead of Christ would] lose their salvation. The warning passages suggest that the readers were being taught with serious Christological-centered instructions describing not go back to the OT ways because Jesus is greater than all.
I find the warning passages very practical and pastoral. They are practical because they are addressing correct way to see Jesus Christ. They are pastoral because they are assisting Christians to live with perseverance and faith during their difficult trials in the first century. Therefore, the challenges by the author of Hebrews carry weighty theological convictions, and must be taken serious. The warnings are figurative and exaggerated parallelism to show the stark contrast between Christ and those who revert back to Judaism.