The doctrine of the Son’s begottenness from the Father is called eternal generation. It is a classic and crucial Trinitarian doctrine, but it also a mystery beyond human description. Eternal generation is like human generation in that one essence begets the same essence, but it is unlike human generation in that it does not involve physical reproduction.

Only Begotten Son of the Father

The Nicene Creed confesses that the Lord Jesus Christ is “the only begotten Son of God.” The Greek word translated “only begotten” is monogenēs, a word used five times in the New Testament with reference to Jesus (John 1:14, 18; 3:16, 18; 1 John 4:9).

While most newer translations render the term “only” or “one of a kind,” the King James Version uses “only begotten” in those five Johannine verses. Whatever the proper translation of the word is in each of those five biblical instances, every English translation I’ve ever seen of the Nicene Creed renders the word “only begotten.”

Let’s think about the names “Father” and “Son.” God is Father because he has a Son; Jesus is the Son because he has a Father. That much should be obvious. And the way in which the Father relates to the Son is by “begetting.” The Father generates the Son, and the Son is “from the substance of the Father” (Creed of Nicaea). One thing we can say about the Father that we cannot say about the Son is that the Father is unbegotten. One thing we can say about the Son that we cannot say about the Father is that the Son is begotten.

Okay, but what does that all mean?

The Arians agreed that Jesus Christ was the only begotten Son of God. This specific language wasn’t the issue. The issue was what those words meant. In a letter to Alexander, bishop of Alexandria, Arius explained that God was “the begetter of his only Son before endless ages; through whom he made both the ages and all that is.” Arius would not have objected to saying, as the Nicene Creed does, that Christ was “begotten of his Father before all worlds.” But in the letter to Alexander, Arius also argued that the Son, “timelessly begotten by the Father,” was “created and established before all ages” and “did not exist prior to his begetting.”1 To counter this position, the Nicene Creed made four further statements in definition of “only begotten.”

The Son is “God of God.” The phrase “God of God” is not a superlative like “Holy of Holies” or “King of kings” or “Lord of lords.” The “of” here might better be translated “from,” speaking of derivation. Jesus Christ is God from God, and the fact that God is used in both halves of the formula suggests that the Son is the same kind of God as the God from which he comes. The phrase also communicates that the Son is not a part of God. He is wholly God of wholly God. The generation of the Son does not imply the division of the Godhead or the multiplication of deities.

The Son is God; the Father is God; the Son is of the Father (the Father is not of the Son); and there is only one God. The Son is “Light of Light.” This claim is similar to the last, but not identical. Here we are dealing with a term rather than a title of divine identity. The argument is that if the term light means the same thing with both the Father and the Son, then they must both be of the same essence. The Son is not a different kind of light than the Father.

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