As far as I can see, Cherylu, the only argument given in the New Testament with respect to the conditions for the effectiveness of Jesus’ atoning death is that he was faithful (Rom. 3:22-25), that he made himself of no account and was obedient unto death (Phil. 2:7-8), that he did not give in to the temptation to avoid suffering (Heb. 4:15), that he learned obedience (Heb. 5:9), that he was “holy, innocent, unstained, separated from sinners (Heb. 7:26-27).
The New Testament is not interested in some absolute state of sinlessness—the emphasis is everywhere on his complete obedience to his Father in following a path of suffering. I cannot for the life of me think how you would justify the claim biblically that he had to be God in order to die for the sins of the world.