@ATG, if Jesus is NOT the spotless Lamb of God (1 Peter 1:17-21) who was crucified and then died to atone for our sins and redeem us from them (so that our sins could be forgiven and we could be saved), in what (other) way, then, do you believe that our sins can be atoned for
I wouldn't know. If anyone is saying Jesus is NOT the spotless Lamb of God, then you can ASK them.
who was crucified and then died to atone for our sins and redeem us from them (so that our sins could be forgiven and we could be saved),
Now, if all He did was die on a cross by hands of men, then He would only be another righteous man wrongly executed by false accusation.
Only with His resurrection from the dead is Jesus Christ the spotless Lamb of God forgiving and atoning and saving us from sinning, that repent from our sins and trespasses against Him:
Rom 4:25
Who was delivered for our offences, and was raised again for our justification.
Rom 10:9
That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
The atonement of sacrifice is not made by killing the lamb alone, but also by sprinkling the blood upon the people.
Heb 9:18
Whereupon neither the first testament was dedicated without blood, For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and of goats, with water, and scarlet wool, and hyssop, and sprinkled both the book, and all the people. Saying, This is the blood of the testament which God hath enjoined unto you.
Only by resurrection from the dead can the spotless Lamb of God sprinkle us with the blood of His eternal Spirit, to atone for our sinning against Him at the cross.
1Pe 1:18
Forasmuch as ye know that ye were not redeemed with corruptible things, as silver and gold, from your vain conversation received by tradition from your fathers; But with the precious blood of Christ, as of a lamb without blemish and without spot:
1Pe 1:2
Elect according to the foreknowledge of God the Father, through sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ: Grace unto you, and peace, be multiplied. Blessed be the God and Father of our Lord Jesus Christ, which according to his abundant mercy hath begotten us again unto a lively hope by the resurrection of Jesus Christ from the dead,
Thanks 
~Deuteronomy
p.s. - our sins are imputed or reckoned or credited to the Lord Jesus's account by God, in the same way that God imputes, reckons or credits the Lord Jesus' righteousness, the righteousness of God, that is, to our accounts.
And so, we see how rejecting the prophecy of Scripture of who imputed Jesus with sin and guilt, leads to the false tradition and lie of men against God, that the Father imputed His only begotten Son with sin on the cross.
Isa 53:34
He is despised and rejected of men; a man of sorrows, and acquainted with grief: and we hid as it were our faces from him; he was despised, and we esteemed him not. Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted.
Despised and rejected of men, not of God. Faces of men hid from Him, not God. Esteemed guilty of sin and smitten of God by men, not God.
And as elsewhere, such false tradition also ends in self-contradiction: If God imputing with sin, does not make anyone a sinner, then God imputing with righteousness, does not make anyone righteous.
If God imputing with sin, does not make anyone a sinner, and imputing with righteousness, does not make anyone righteous, then imputation of God is made of none effect upon anyone on earth.
Jesus was never a sinner but, for a brief moment in time, He stood in our place ~as one~ (on the Cross) FOR us,
Already corrected enough times.
according to His Father's predetermined plan and will, to redeem us and finally make forgiveness and salvation a reality for us!
Finally by His resurrection from the dead at the right hand of God, not by His death alone at the cross.