Proponents of Eutychianism managed to avoid full-on docetism, because unlike the docetists, the Eutychians did not say that the body of our Savior was merely an illusion. However, by teaching that the deity of Christ absorbed His humanity, they ended up effectively denying that Jesus possesses a true human nature and a true divine nature. They give us a Jesus who is a mixture of humanity and deity, not truly God or truly man.
Eutychianism was not the only Christological heresy in the early church to tend toward a kind of docetic denial of Christ’s true humanity. The heresy known as Apollinarianism also denied the true humanity of Jesus. Apollinarianism is named after Apollinaris, the fourth-century bishop of Laodicea. Early in his career, Apollinaris was highly esteemed by such orthodox Christian thinkers as Athanasius of Alexandria because of his staunch defense of the Council of Nicaea and its affirmation of the full deity of Christ. In his later ministry, the orthodox party opposed Apollinaris because of what he taught about the relationship between the human and divine natures of Christ.
Apollinaris believed human beings are made up of three constituent parts—a physical body, a “lower” soul that makes us living creatures, and a “higher” soul or spirit that is equivalent to the rational mind that humans possess. Immediately, we should see problems with Apollinaris’ thinking, as this three-part division of human beings has no scriptural support. Biblical Christianity has always taught that human beings have two constituent aspects—body and soul (dichotomy). This understanding is grounded in passages such as Matthew 10:28, which refers to human beings as possessing only a body and a soul.
Having adopted a erroneous view of human nature, Apollinaris said that in the person of Jesus Christ, the Logos or divine aspect of the Savior replaced His “higher” spirit. Jesus, then, had a human body, a “lower” human soul, and a divine spirit. Apollinaris effectively denied that the seat of rational thought in our Savior is truly human. He compromised Jesus’ true humanity by denying that He possesses a human mind or soul, since the human mind or soul is an essential component that makes human beings human. And, by compromising Jesus’ humanity, Apollinarianism gives us a Savior who cannot save us. Animal sacrifices could not truly atone for sin because they are not human (Heb. 10:4). If Jesus does not possess a human soul, then He is not truly human, and thus cannot atone for the sin of other humans.