Know Your Christological Heresies- Apollinarianism 
The Heresy: Apollinarius was a bishop in Laodicea in the late 300s. He taught that the person Jesus had a divine nature (mind and spirit), but a human body. Apollinarianism (sound it out slowly with me... a-poll-in-ar-i-an-ism) asserted that when the incarnate Son of God became the man Jesus, the divine nature of the Son of God was united with a human body, but not a human mind. You could look at it as the divine, immaterial part of the Son being placed in a human, material shell. Thus, this view has been called the ‘God in a bod’ theory. Apollinarianism: Jesus = human body + divine mind and soul.
Why It Was Proposed: Apollinarius was concerned with establishing the true divinity of Christ. Specifically, he was responding to Arianism (we’ll cover this soon), which taught that the Son of God was created by God the Father, and was therefore a lesser form of God. Apollinarius combated this view by seeking to affirm the true and full divinity of Jesus, which led him to deny the human mind and soul of Jesus. It was a noble motive, but he whiffed on the execution.
Why It Is Wrong: The Bible is clear that Jesus had a human mind and soul. Luke 2:52 says that Jesus increased in wisdom. Divine minds don’t increase in wisdom (God is pretty much eternally maxed out in the wisdom department, making growth nonsensical), so Jesus must have had a human mind/soul.
This was of greatest concern to the church: if Jesus did not have a human mind/soul, then Jesus did not die for our human minds and souls. Gregory of Nazianzus said; “That which was not assumed was not healed.” That is, to be our perfect substitute and sacrifice, Jesus must have been fully human in every way we are, both materially and immaterially. Every part of the human fell in Adam, so every part of the human needs saving, therefore Jesus must have been human in every way, material and immaterial. By the way- this Gospel concern that Christ be like us in every way, that he might be our Savior, will be a theme that runs throughout the early church’s theological wrestling over Christology.
The early church also denied Apollinarius’ premise that two natures (human and divine) could not be united in one person. Apollinarius thought Jesus as a person could not have both a fully human and fully divine nature. But this is exactly what the early church affirmed (as mysterious as this might be). Apollinarianism was rejected and condemned as a heresy at the Council of Constantinople in 381.
Why It Matters: The biggest reason it matters is the Gospel reason above- if Christ wasn’t human in every way, He could not be our Savior in every way. If only Jesus’ body was human, then he would only be a savior for the human body. But our minds, souls, wills, spirits, emotions, and all our immaterial faculties need saving. We know this because we’ve all been to the DMV.
Furthermore, if Jesus did not have a human mind, then He could not have known completely what it is to be human. He could not have felt our sorrows and joys and struggles and elations and temptations and despairs. He would not have been our ‘Hebrews 4:15’ sympathetic high priest, able to sympathize with our weaknesses and tempted in every way we are, yet without sin.