What is the scriptural basis for the belief that a man is not capable of being the Saviour?

Mike Borden provides a thought-provoking answer to the question According to the Protestant denominations that hold to the doctrine of clarity of scripture, is Trinitarianism clear? . He says that > Simply put Trinitarians are convinced from Scripture by natural > apprehension and spiritual illumination of what is written that a > Jesus who is not the only begotten Son of God, the Logos who was God > in the beginning and never ceased to be God during the incarnation, **is > not capable of providing salvation** to all mankind because the chasm > between God and Man is uncrossable to Man. Therefore trinitarian > belief is considered necessary for salvation because a merely human > Jesus cannot save and man, unaided by the Holy Spirit, cannot > apprehend salvation. According to this line of thought, it isn't that Trinitarianism is directly clear from scripture, but rather that it is clear from scripture that salvation from a 'mere man' is not possible, and rather requires the Savior to be God Himself. Therefore, the Savior must not be a mere man. In a more formal style, it is 1. It is clear from scripture that salvation cannot come from a mere man but instead requires the Saviour to be God. 2. It is clear from scripture that salvation comes from Jesus. 3. Therefore, it is clear from scripture that Jesus cannot be a mere man but rather is God. Yet, 1. seems questionable. Consider Romans 5:15-19. > 15 But the gift is not like the trespass. For if the many died by the > trespass of the one man, how much more did God’s grace and the gift > that came by the grace of the **one man, Jesus Christ**, abound to the > many! 16 Again, the gift is not like the result of the one man’s sin: > The judgment that followed one sin brought condemnation, but the gift > that followed many trespasses brought justification. 17 For if, by the > trespass of the one man, death reigned through that one man, how much > more will those who receive an abundance of grace and of the gift of > righteousness reign in life through the one man, Jesus Christ! > > 18 So then, just as one trespass brought condemnation for all men, so > also one act of righteousness brought justification and life for all > men. 19 For just as through the disobedience of the one man the many > were made sinners, so also **through the obedience of the one man the > many will be made righteous.** Similarly, consider 1 Corinthians 15:21-22. > 21 For since death came through a man, **the resurrection of the dead > comes also through a man.** 22 For as in Adam all die, so in Christ all > will be made alive. So, what is the basis for 1. above - what is the scriptural basis for the claim that the Saviour cannot be a mere man? Note: this isn't asking about the scriptural basis for the idea that Jesus is God. For the purposes of this question, I'm taking as given that that isn't directly clear enough to qualify under the doctrine of clarity of scripture. (You can of course disagree with this, but that's another question, namely the one linked at the beginning of this question.) Rather, it's asking about the basis for the Saviour **necessarily** being God, whether Jesus is God (and man) or simply a man.