Here is a good explanation on this issue:
"When Jesus would uplift men to become members of the heavenly family, He humbled Himself to become a member of the earthly family, and by partaking of our nature He became the Son of man, the Son of Adam, and a Brother to every son and daughter of our fallen race."--Ms 58, 1896, p. 4. {17MR 25.3}
"The two expressions human and divine were, in Christ, closely and inseparably one, and yet they had a distinct individuality." {ST, May 10, 1899 par. 11}
"The nature of God, whose law had been transgressed, and the nature of Adam, the transgressor, meet in Jesus--the Son of God and the Son of man..." {17MR 338.1}
Why the question of Christ’s Nature is vital to us.
Papal Rome teaches that Jesus did NOT take our fallen nature but possessed a human nature different to ours. She claims that possessing a fallen nature is itself a sin and therefore teaches that Christ could not possess it. Rome teaches the doctrine of the “Immaculate conception of Mary” - that she was miraculously given a sinless nature, a nature unlike ours, so that Jesus inherited a sinless “human” nature from her.
Today many Protestants effectively teach the same thing. Like Catholics they claim that merely possessing a fallen nature is sin. The only real difference between Roman Catholic theology and so-called Protestant theology is that the Protestant view claims that instead of God miraculously giving Mary an unfallen human nature, God gave Jesus an immaculate unfallen human nature, or some unique hybrid nature that we do not possess. Many modern day Seventh Day Adventists in contrast to our forefathers have been promoting similar sentiments.
Had Christ lived his earthly life in any nature other than our fallen nature then He would have failed to condemn sin in our fallen nature and would have failed to demonstrate what is possible in our fallen nature. Christ lived a life of sinlessness in our fallen human nature and thereby condemned sin in the flesh, in our flesh. Christ proved that our nature is no excuse for sinning and that obedience to God’s law is possible in our fallen nature thus exposing Satan’s lie and charge against God : “Satan, the fallen angel, had declared that no man could keep the law of God after the disobedience of Adam. He claimed the whole race under his control.” {3SM 136.1}
The only way that Christ could demonstrate how, we in our sinful nature, might live sinless lives is by himself living a sinless life in our sinful nature.
“He [Christ] came with such a heredity to share our sorrows and temptations, and to give us the EXAMPLE OF A SINLESS LIFE.” E.G. White, Desire of Ages, p49.
“He sent His Son to this world to bear the penalty of sin, and to SHOW MAN HOW TO LIVE A SINLESS LIFE.” E.G. White, Reflecting Christ, p37.
“He came to this world and lived a sinless life, that in His power His people might also live LIVES OF SINLESSNESS.” E.G. White, Review and Herald , April 1, 1902
“He placed us on vantage ground, where we could live pure, SINLESS LIVES.” E.G. White, Signs of the Times, June 17, 1903.
“Every one who by faith obeys God’s commandments, will reach the condition of SINLESSNESS in which Adam lived before his transgression.” E.G. White, Signs of the Times , July 23, 1902.