Literally no one here is arguing that works is what saves. If anyone thinks that, you aren't paying attention. But that also means, we
are advocating for "must" but in a nuance way that I don't think you're understanding if you automatically equate it to "adding to His sacrifice".
As a Messianic, the Christian doctrine seriously lacks understanding in how the sacrificial system worked and what the point of it was and how that ties into Christ. The majority of what is being taught, is incorrect. Specifically if you equate to adding works to trampling the Blood of Christ.
Let me be clear... Sacrifices NEVER took away sins. The book of Hebrews backs this up. Please stop perpetuating this lie. To understand what Christ did on the cross, you have to let go of the idea that His death was a ritualistic sacrifice. It wasn't by nature. Which makes the whole thing convoluted and brings you to wrong conclusions if you think it was.
- God's universal law: The wages of sin is death. Sin separates us from the Father. That is the universal problem that had to be dealt with. Look at Lucifer and all the angels that left. Iniquity (sin) was found in him. So if sin is transgression of God's law, then God's law is universally applied, not just strictly towards humans. Revelation 6 shows an altar (where you sacrifice) in heaven. Revelation 9, depicts a golden altar in heaven. Revelation 11 shows there is a temple of God and there is an altar. If the sacrificial system was a means of dealing with sin, why is there an altar and temple in heaven?
- Temple sacrifices: These are offerings (korban literally means "to draw near"). They are gifts brought to God as a means of reconciliation. The sacrifice itself is not what forgives sin, it is a means of drawing near to God and seeking His forgiveness which God automatically promises He will forgive if it's due to sin.
- Christ's death: Christ took upon Himself the universal penalty of sin...death. He satisfied that universal consequence so that we no longer have to bear it ourselves. His death addressed the separation caused by sin, opening the way back to the Father. God's spirit which we had originally when Adam and Eve were created, but left after sin tore us apart (The Holy Spirit). This is why there was a warning that you will die if you eat from the fruit. It wasn't just literal death eventually, it was immediate spiritual death (Being spiritually dead is a concept scripture talks about several times).
So if your deduction is that obedience somehow adds to the sacrifice Christ did, that literally makes no sense considering it was disobedience that put him on the cross in the first place. And only through God's grace are we forgiven of sin. Like Soy said, if we were perfect in the law, we wouldn't have needed Christ but that doesn't mean you trample grace by not striving to do the best you can in obedience. And only those who strive in obedience are called Sons/Daughters of God (1 John 3:7-10, 1 John 2:3-5).