Know Your Christological Heresies- Arianism 
The Heresy: This might technically be more a Trinitarian heresy, but it severely affects how we view Jesus, so we’ll go with it. Arius, Bishop of Alexandria in the early 300s, believed the Son of God was at one point created by God the Father. In his view, the Son and the Holy Spirit are both God, and both existed before the rest of creation, but both were created by God the Father and therefore are not essentially equal to the Father. According to Arius, the Son has not existed eternally.
The Son is still a heavenly being and therefore superior to creation, but he is also subordinate to the Father in his essence. The Son is like the Father, or similar to the Father, but because he is a created being, he is not equal to the Father in nature/essence/being. Arianism: the Son of God ≠ God the Father in nature/essence. Stated another way, there was a time when the Son was not.
Why It Was Proposed: There are some scriptural passages that, at first blush, seem to indicate the Son is indeed inferior to the Father, and even a created being. Colossians 1:15 calls Christ ‘the first-born of all creation.’ Additionally, several passages call Jesus the ‘only begotten Son’ (John 1:14, 3:16), also seeming to indicate that the Son was created by God. There is also John 14:28, wherein Jesus says that ‘the Father is greater than I.’
A significant motivating factor in Arian thought is the desire to maintain the transcendence of God the Father, and the humanity of Christ the Son. In Arian thought, God the Father as God must be totally, completely, unique from creation. God’s divine transcendence must be maintained- it is a given. But, if Jesus is fully God, equal to the Father in every way and essence, yet at the same time authentically human and a part of creation, then the Father’s divine transcendence has been diminished. Furthermore, if Jesus the Son is uncreated, eternal, fully God, and therefore transcendent, then he cannot identify with humanity, which is part of creation. He cannot, at the same time, be fully divine and transcendent, and fully human and part of creation. So, if Jesus is fully God in the way the Father is God, he could not be fully human, and he cannot identify with humanity and die as a human on the cross. The incarnation and salvation of humanity would be an impossibility. This is a Gospel issue for Arius. In his mind, it is impossible to be totally distinct from creation as eternal God, and yet be part of creation and be its savior. What is then needed for salvation is a mediating being, a being that crosses the gap between the transcendent God and created humanity. The Son is the being that crosses the gap, because he is God, yet created God. He is both divine and creation.
Why It Is Wrong: The church concluded that the Son simply isn’t created. The Son was not created by God, but has eternally existed with God the Father. Colossians 1:16-17 is conclusive: “For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities—all things were created through him and for him. And he is before all things, and in him all things hold together.” The meaning is clear- the Son was part of creating everything, and anything that has ever been created was created by, for, and through Christ. So, the Son stood outside of all creation before he entered into it to save it. This makes Arius’ conclusion false. The Son is not a created being, and has existed eternally right alongside the Father and Spirit, fully God and equal in essence.
Additionally, many passages affirm the full divinity of Jesus the Son of God. See Matthew 28:19, John 1:1-5 (notice the Son’s eternal existence with the Father, having life in himself), Hebrews 1:1-3, 2 Corinthians 13:14, and 1 Peter 1:2. For further convincing, carefully read through Revelation 4-5, and notice that people worship the Lamb in the very presence of God the Father. The fact that they aren’t wiped out on the spot is a pretty clear indication that Jesus is fully God, and worthy of worship even in the eyes of the Father.
So what about Colossians 1:15 which calls Christ the firstborn? This verse is not saying Christ was created, but that Christ has the authority and superiority of a first-born son. Christ has primacy in relationship to creation. Roughly the same thing can be said about the ‘only-begotten’ passages. Whatever those passages mean, they cannot mean Jesus was created at some point. These passages are speaking of Jesus’ unique relationship to the Father and privileged place in relationship to creation.
Arianism was first condemned in the Council of Nicea in 325. There Christ was described as “the Son of God, begotten of the Father, the only-begotten; that is, of the essence of the Father, God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father…” Though Arianism was condemned formally at Nicea, there was still much wrestling over the issue until it was more fully and finally denied at the Council of Constantinople in 381.
Why It Matters: This is all about affirming the divinity of the Son. Is Jesus God? The answer must be yes, full stop. The Son is God just as much as the Father is God. This makes the incarnation all the more remarkable! The Son was not in any way like us, but by miracle and mystery and humility became one of us. The Son’s condescension and incarnation is maybe the greatest truth in history. Certain faith groups (Mormons, Jehovah’s Witnesses, and Unitarians) deny this truth and still teach that Jesus was a created being, adhering to the Arian heresy long ago condemned by the Christian church. The eternal Son’s full divinity is one of the central tenets of orthodox Christianity, and a truth we must always maintain and cherish.