Christ died once and for all sins, correct. And we receive His sanctifying grace, which flows from His Sacrifice on Calvary.
This is where some Christians differ from the Historical Christian Church. Some believe the pascal mystery is only in the past. We believe that it is made present.
Hebrews 10:10 is referring to the fulfillment of the Old Covenant Sacrifices. Jesus is both the High Priest and the Sacrificial Lamb and He offers Himself to the Father on our behalf.
Hebrews 10:11 contrasts how the Old Covenant Priests would make new sacrifices over and over again. Catholic/Orthodox Christians do not offer new sacrifices.
The one, eternal, and unchanging Sacrifice of Calvary is made present in the perpetual Offering by Jesus Christ, who sits at the right hand of God (verse 12).
Hebrews 10:14 again points to the perpetual nature of His Sacrifice and the perfect fulfillment of the Old Covenant. No other sacrifices will nor can ever be greater than the Holy Eucharist!
Colossians 2:13 also points to Christ’s fulfillment of the Old Covenant.
In Baptism, all our sins are forgiven (both original sin & actual sin).
St. Peter, in 1 Peter 3:21, also talks about how Baptism is the means by which we enter into Covenantal relationship with Jesus Christ.
And like Hebrews 10:12, 1 Peter 3:22 refers to Christ, who is sitting at the “right-hand of God.”
1 Peter 4:12 speaks of how those who are born anew should live for the will of God and not for human desires. As you can see, sin still matters. I am not implying that they believe sin doesn’t matter, but their reformed theology kind of supports the idea that sin doesn’t matter.
This is in response to a meme going around Twitter that tries to use the above verses to prove “Once Saved, Always Saved” theology vs. their misunderstanding of historical Christianity, which the Catholic & Orthodox still hold true today.