On what basis was Jesus’ death sufficient for redemption according Non-Trinitarians who maintain that Jesus was not eternal God as God the Father is?

According to Biblical Unitarians...

Jesus' death is sufficient because he is fulfilling prophecies that spoke of a man to come and not God or anything else. Ps 22 speaks of Jesus and he fulfilled this - reciting the first and last lines on the cross.

Gen 3:15 speaks of the seed of the woman - a human, revealed as the second and last Adam - another human. How could a second Adam be God? This is not expressed anywhere.

Isaiah 53 speaks of the suffering servant. A prophecy of the one to come.

• He grew up before Him like a tender shoot, and like a root out of dry ground
• He was pierced for our transgressions, he was crushed for our iniquities;
• He was led like a lamb to the slaughter
• For he was cut off from the land of the living
• He had done no violence, nor was any deceit in His mouth
• He has poured out His life unto death

There is no biblical precedent for Jesus' sacrifice/offering to be God. None! There IS a precedent for the offering to be without fault and blemish - this is driven home throughout the OT and affirmed in the NT. Lev 23:12, 9, Num 6:14

you were not redeemed with perishable things like silver or gold from your futile way of life inherited from your forefathers, 19but with precious blood, as of a lamb unblemished and spotless, the blood of Christ. 1 Peter 1:18-

The foundation for a Jesus is God construct is based on an incarnation. This is an unbiblical idea not taught, believed, or spoken of in the entire bible. And so the whole idea of God having to die for our sins is also unbiblical - relying on suppositions and theories, opinions.

Psalm 2 points to this one who would be the son of God.

the LORD and against His Anointed, saying... 6“But as for Me, I have installed My King Upon Zion, My holy mountain.” 7“I will announce the decree of the LORD: He said to Me, ‘You are My Son, today I have fathered You.

Jesus was without fault and spiritually perfect, being without sin - being the son of God and not with a human father which Paul shows is the means for inheriting a corrupted nature. (Adam was also a 'son of God' - was he God too?)

just as sin entered the world through one man, and death through sin, so also death was passed on to all men, because all sinned. Rom 5:12

death reigned from Adam until Moses, even over those who did not sin in the way that Adam transgressed. Rom 5:14

He could only be perfect - w/o sin, if he was born outside of the sin of Adam (Rom 5) which he was, as his Father was God, not Joseph. The whole deal of Jesus, the man, being foreknown by God and already 'slain' figuratively was always part of God's plan of redemption before the first sin happened. So he has appeared ‘in these last days’ (Heb 1) to begin accomplishing God's plan of salvation prophesied throughout the OT.

1 Pet 1:20 For He was foreknown before the foundation of the world, but has appeared in these last times for the sake of you

IF Jesus was 'God' he couldn't be tempted as we are, able to sin as we do, or die as we do. He was raised to immortal life as all who believe in him will also be.

Quoting from Nigel in a comment:

The death of Jesus Christ, in redemption, is his departure from the body. The eternal Son cannot die.

What verse speaks of an 'eternal Son'? What verse speaks of 'departure from the body'? Being not from the bible, these ideas are foreign to the word of God and form the basis for all manner of strange beliefs.

As Isaiah describes in great detail - no "eternal Son" in view there - nor anywhere else!

Certainly we do have an eternal son now that Jesus is raised, exalted and given life by the Father - life he did not have before being 'mastered by/subject to' death Rom 6:9 and 1 Pet 3:18 "having been put to death indeed in the flesh, but having been made alive in the spirit"

For as the Father has life in himself, so he has granted the son also to have life in himself. John 5:26

When God 'gave His only son' He meant it! He didn't give 1/2 a son in a flimsy mock-up human sacrifice while an alleged eternal Son remained untouched by the whole ordeal.

As the last Adam, Jesus, being without sin, is perfectly sufficient to cover the sin of all men and to redeem his Father's creation from the results of Adam's sin and the adversary’s deception because all are included by God's grace.

Jesus’ death was sufficient because he was without sin... as Hebrews 10 sets out in abundant detail.

The consistent expression of ‘flesh’ and ‘blood’ are components of man, not God.

...we have been sanctified through the sacrifice of the body of Jesus Christ once for all. Heb 10:10

Yet many seem to read, 'body of God' with an incarnation in mind.

Most probably understand the basics of OT sacrifice/worship. The priest could enter the Holy of Holies only once a year an behalf of the people of God. He had to thoroughly cleanse himself according to God's specific instructions. No one else could enter in - they would surely die! Even the priest would die if he did things wrong - Aaron's sons died because they didn't follow instructions carefully (Lev 10:1,2).

Jesus is now the High Priest - operating constantly for our well-being. His one sacrifice - for all people for all time, far supersedes the old model. He is perpetually clean because of the sinless life he lived in obedience to the Father's will.

Simply, there is NO need or precedent in scripture for God to somehow die. Jesus is presented as a man and a man only, born of Mary ~ 4BC. Anything other is conjecture and reading in that which is not there.

We have the moment when the veil was torn, as Jesus granted us access to the Father like never before (Matt 27:50). There is no more separate 'Holy of Holies' in a physical tabernacle - it is defunct.

Hebrews 10:19 Therefore, brothers, since we have confidence to enter the Most Holy place by the blood of Jesus.

Does God have blood to spill? Can a God/man hybrid with supposed two natures and two lives who is not described at all like this, except in the writings of man, be a worthy replacement for the scriptures that speak of a man only?

In the complete absence of scripture clearly expressing Jesus as God, but very persistently expressing him as a man and by the things he learnt, growing in wisdom and obedience, being tempted and dying - we can only responsibly and faithfully accept God's inspired version of truth and not a made-up version.

God has to accommodate the law. Sin = death. Sin is annulled when a death covers it. We can die for our own sins, but never get raised up again - ever. Jesus, foreknown by God before the world began, is the life that could be raised again, and we in him, because he was without sin.

He was foreknown before the foundation of the world 1Pet 1:20

Jesus is only worthy because he, as a man, was without sin. Having God w/o sin as a sacrifice is nonsensical. Of course God is so, but a man who had to resist the greatest of all temptation and NOT succumb - now THAT is something! No wonder god says, 'let all the angels worship him'!

Give him the honour he deserves and not strip him of his magnificent accomplishments by making him a God/man who could not fail, who could not sin and who could only 1/2 die!

Of course, God is without sin, and unable to be tempted or die - how then is Jesus tempted if he could not sin? He already said he came, ‘not to do my own will, but the will of God’ John 6:38. Having a differing will makes him clearly not God! How can God have two wills?

The odd construct that an 'angel' could suffice is nonsensical in that they would NOT be an 'Adam' as Jesus was. A man to battle the adversary (seed of a woman Gen 3:15) is a fair deal. For the devil to battle God is also nonsensical - it would be called a foul. God does not need to stack the deck - ever!

https://www.biblicalunitarian.com/articles/why-did-jesus-have-to-suffer-and-die https://www.biblicalunitarian.com/articles/in-the-book-of-revelation-god-is-not-the-lamb-and-the-lamb-is-not-god

This is from the perspective of Jehovah's Witnesses. A full explanation of Jesus' ransom sacrifice can be found in chapter 5 of the book, "What Can the Bible Teach Us?"

1 Corinthians 15:21, 22 (NWT)

For since death came through a man, resurrection of the dead also comes through a man. For just as in Adam all are dying, so also in the Christ all will be made alive.

Jesus' death is sufficient for redemption from sin on the basis that Jesus was a perfect man, without sin, just as Adam had been.

When Adam was created, he was perfect, but when he disobeyed God, he became sinful, selling himself and all his children to sin and death. (Romans 5:12; 7:14) In order for Jehovah God to have a legal basis to repurchase mankind, forgive sins, and restore humans to a perfect state with the opportunity to live forever, there must be a corresponding ransom to replace the life that Adam lost, one who lives their whole life without sin, obedient to God. (1 Tim. 2:5, 6; Romans 5:19) No descendent of Adam can serve as this ransom because we are all born sinful, imperfect. (Psalm 49:7, 8)

To provide the ransom, Jehovah miraculously caused one of his perfect spirit sons to come to earth as a human. (1 John 4:9; Luke 1:35) This was Jesus. Jesus remained obedient to God until death. Later, when Jesus returned to his Father in heaven, he presented the value of his perfect human life to Jehovah as the ransom. (Hebrews 9:24) Furthermore, Jesus disproved Satan's accusation that no human would remain obedient to God if that person was severely tested. (Job 1:9-11; Prov. 27:11)