Hello Whigumstyx, and welcome to Worthy.
I think you are referring to the following verse:
For if we sin willfully after we have received the knowledge of the truth, there remaineth no more sacrifice for sins.
This is one of the three favorite verses that those who think one can lose their salvation point too, and on the surface it looks like they are right. But look at the whole chapter of Hebrews 10, and you will find out a different story. If one looks at Hebrews 10:12-18, we see that Jesus death and resurrection was the last and final sacrifice that God demanded.
Now where remission of these is, there is no more offering for sin. Hebrews 10:18 One need to remember that the Book of Hebrews was written to Messianic Jews/ Jews who where Christian trying to decide do we stay in the Law/Old Testament sacrificial system or not. The writer of Hebrews is stating that Christ Sacrifice was the final and only sacrifice that God the Father would now accept. So the writer goes on in to say if one goes back to animal sacrifices after accepting the Sacrifice of Jesus the True Lamb of God, one could only have fierce wrath in his/her future. No doubt the Jews who came to Jesus where still being pressure to honor these sacrifices, but to do so would be to be choked by the thorns/cares and riches and pleasures of this life (Luke 8:7, 14). This would be despising the Blood of the Covenant. Of how much more severe punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the Blood of the Covenant, by which he was sanctified, an unholy thing, and hath done despite to the Spirit of Grace. Hebrews 10:29 Jesus Christ is God True Hallmark Card to us, God care enough to send the Very Best. Would not the Godhead Trinity have every right after redeeming us, to state no more, Jesus Blood, was the end to all Sacrifices, you cannot add to True Perfection. Peter even states we are Redeem with the Precious Blood of Christ, I Peter 1:18-19.
We also know of assuredly that faith is how the just shall live, faith in the finish work of Christ, but to try to add to this True Perfection is to draw back, Hebrews 10:38.
I should also state many in OSAS camp will probably agree with this, but those who think one can lose their salvation will not agree.