First of all, denominations don't matter. Consider that in the laws handed down by God, the tribute required to atone for sacrifice was the blood of an animal, without defect. Okay? So that's cause and effect. Sin requires a payment.
By Gods own rules, man must atone for his sins, with blood. The variance of that blood payment depends on the nature of the sin committed.
Again, playing by Gods own rules, sending a human man, inhabited by the glory and spirit of God in Jesus Christ, would cover the sins of mankind. But only if a blood sacrifice was made. Jesus said that only through him salvation could be found.
So consider then that if that sacrifice (which follows Gods own rules), was not enough to completely atone for a confessors sins, then why bother? What is the point of the cross and of the resurrection of Christ, if man must continue to strive and perform works to keep his salvation?
It's simply not logical or theological. It denies the power of the cross, the divinity of God and ignores the rules that God himself has played by since sin entered the world.
Furthermore, God doesn't say anywhere that man should live like they have carte blanche and do whatever they want. Christians are still called to a life of holiness and sanctification. Not because we need it to save ourselves, but because it's right and commanded by God, but also because it sets us apart in the world and demonstrates to others how we live. As Jesus said, we will be known by our fruit - our actions, our deeds, and our examples.
This argument over demonstrations and traditions and pointless. The cross is sufficient because it is freely given by God to those would accept it. God is mighty enough that we need not lean on anything else but the blood of Jesus, sacrificed ONCE FOREVER, for salvation.
All else is religion - a false idol propagated by fallen men for their own purposes.
