The writer of the letter to the Hebrews is actually speaking about the giving of the law on Mount Sinai. The context makes that clear as the verses go on.
God gives his law and we do the opposite. He has commanded us to live with honesty and integrity, and we lie and practice deceit, lying in all forms from barefaced lying to white lies, excuses, and exaggerations that are not true. People are lying all the time; deceit and dishonesty is right through the human heart. The Greek word for disobedience is different again and it means something like this: simply not hearing or disregarding the different ways of obeying God. So we have here, doing the very opposite of what he commands, and just paying no attention to his commands. Not regarding them as important or significant in our lives.
This is calculated to shock us and make us think. Without the mercy of Christ we shall all face judgement, and be eternally punished for our sins. But perhaps you have another sin looming over even your sin against the standards of God, and this sin is that you rejected or neglected so great salvation. It meant nothing to you; you didn't want it; you didn't need it. This guilt is in a category that eclipses all the other sins. How shall we escape? – ‘run-out’ is the Greek, runaway. It's almost as though you've been caught red-handed in a crime and you have been arrested and handcuffed, and the police van comes and you are put in the back and the door slammed behind you. There is no escape. It's too late. When it comes to the end of life’s journey, how can you escape? You’ve not only sinned your way, all the way to judgement, but you’ve got this other terrible thing to account for. You've insulted Christ and in pride you've rejected the way of mercy and forgiveness and kindness and salvation. What a foolish thing to do, what an insulting thing to do to God!