After we confess that “we believe in one Lord, Jesus Christ” there is a string of phrases intended to articulate the full divinity of the Son of God and his unique relationship to God the Father: “the only-begotten Son of God, eternally begotten from the Father, Light from Light, true God from true God, begotten, not made, of the same substance as the Father.” In this note, I consider that final phrase, “of the same substance as the Father.”
The Greek word translated “same substance” is homoousios, which is a compound word: homo “same” and ousia “substance, essence, or being.” This word is not found in Scripture. Thus far the creed has used biblical language to confess the full divinity of the Son, but with this phrase, a non-biblical word is used.
The use of this word homoousios was the source of much controversy among church leaders in the fourth century. Some argued for the term, some argued against it, and some argued for modification. (The proposed alternative was homoiousios, meaning similar in being; homoi “similar” rather than homo “same.” This led Edward Gibbon to characterize the debate as a furious contest over a diphthong. Yes, it’s only an “i,” but one letter can make a big difference, like whether someone runs a business or ruins a business.) When the creed was revised at the Council of Constantinople in 381, the phrase remained. The Son is “of the same being as the Father.”
The word homoousios expresses the essential unity of the Father and the Son and the Spirit. God’s attributes are essential. For example, God does not have or acquire righteousness. He is righteous in his very being. He is righteousness. The Son and the Spirit are of the same being as the Father, which means the Son and the Spirit share one and the same holiness, life, knowledge, wisdom, will, power, authority, and glory with the Father.
This is why the creed goes on to confess that the Holy Spirit is worshipped and glorified with the Father. The term homoousios guards the integrity of our worship. We confess that the Son is “of the same being as the Father” because all creation sings: “To him who sits on the throne and to the Lamb be blessing and honour and glory and might for ever and ever!” (Revelation 5:13)