The necessity of Jesus Christ being man - fully human no different from us - yet without sin, is essential to God's salvation of man through Christ's life and death. Jesus took no divine short-cuts or easy roads as our substitute (nor could he if he was to be the Lamb of God that taketh away the sin of world) in either his obedience as a man to his Father or ultimately in his suffering and dying for us on the cross.
Dr. R. Scott Clark addresses question and answer #17 from the Heidelberg Catechism in his post That He Might Bear in His Humanity:
17. Why must he also be true God?
That by the power of His Godhead He might bear in His manhood the burden of God’s wrath, and so obtain for and restore to us righteousness and life.
1 Isaiah 53:8. Acts 2:24. 2 John 3:16. Acts 20:28. 3 I John 1:2.
Dr. Clark writes: It is with these categories in mind that the Heidelberg Catechism says what it does about the Son bearing in his humanity the wrath of God against sin. We need a substitute and he must be like us in every respect, sin excepted (Heb 4). This is why we speak of “consubstantiality.” He must be one of us. He cannot merely appear to be like us. Why not? Because it was one of us, created in righteousness and true holiness, who sinned, who violated God’s law and incurred the greatest penalty...
... Of course Jesus was more than just a teacher. He was our Mediator and substitute. He came in our place. He came, was incarnate, was born, obeyed, died, and was raised for us (Rom 5:8). That prepositional phrase “for us” says it all.
Read the entire post.
Some relevant scripture passages:
Hebrews 2:17 Therefore, He had to be made like His brethren in all things, so that He might become a merciful and faithful high priest in things pertaining to God, to make propitiation for the sins of the people.
Hebrews 4:14 For we do not have a high priest who is unableMd to sympathize with our weaknesses, but one who in every respect has been tempted as we are, yet without sin.
Hebrews 7:26 For it was fitting for us to have such a high priest, holy, innocent, undefiled, separated from sinners and exalted above the heavens;
2 Corinthians 5:21 He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him.
5b Christ Jesus,
6 who, although He existed in the form of God, he did not regard equality with God a thing to be grasped,
7 but emptied Himself, taking the form of a bond-servant, and being made in the likeness of men.
8 Being found in appearance as a man, He humbled Himself by becoming obedient to the point of death, even death on a cross.
9 For this reason also, God highly exalted Him, and bestowed on Him the name which is above every name,
10 so that at the name of Jesus EVERY KNEE WILL BOW, of those who are in heaven and on earth and under the earth,
11 and that every tongue will confess that Jesus Christ is Lord, to the glory of God the Father.
ALMIGHTY God, who hast given us thy only-begotten Son to take our nature upon him, and as at this time to be born of a pure virgin: Grant that we being regenerate, and made thy children by adoption and grace. may daily be renewed by thy Holy Spirit; through the same our Lord Jesus Christ, who liveth and reigneth with thee and the same Spirit ever, one God, world without end. Amen. [The Collect for Sunday after Christmas-day]