The most obvious evidence for the doctrine of the eternal generation of the Son is the biblical assertions that (1) the Son is begotten of the Father and (2) He is the only begotten Son of God. In the modern era difficulties have been raised with both these apparent supports for eternal generation.
As to # 1, let me say this. Psalm 2:7 asserts, “I will surely tell of the decree of the LORD: He said to Me, ‘You are My Son, Today I have begotten You.'” This verse is quoted a number of times in the New Testament (Acts 13:3; Hebrews 1:5; 5:5). Modern scholarship has noted that this language speaks of the enthronement of the Son of David as the King of Israel and is applied in the New Testament to the resurrection of Christ. It has concluded from this that there is no reference in it to a so-called eternal generation of the Son. While I am of the opinion that the historical sonship of Christ actually is intended to reflect and incarnate His eternal sonship, I grant that these verses are not clear proofs by themselves of eternal generation.
As to # 2, I believe this argument is capable of solid support. The word frequently translated “only begotten” in the Bible is the Greek word monogeneis. Until the modern era it was assumed that this word was derived from two words, “only” and “begotten,” and meant “only begotten.” This derivation and meaning has been challenged by modern scholarship. It derives the word from “only” and “kind” and affirms that the word means one of a kind or unique with no connotation of having been begotten. Thus, the ESV translates monogeneis simply as “only” in the major passages where it is used of God’s Son. Though the ESV is really popular right now, I must confess that its adoption of the modern explanation of monogeneis makes me really unhappy. This is not because I am certain that the old derivation and translation of the word as only begotten is certainly correct. I think a good case can be made that it is! And so does Lee Irons and John Frame! But my unhappiness is rooted in the fact that I am quite confident that “only” is a really lame and inadequate translation of the word. Here’s why.
(1) Monogeneis is used 23 times in the LXX and NT. In 19 of those occurrences the idea of begetting is clearly suggested by the context. It is used with son, daughter, and father. The other four occurrences are figurative and cannot be normative for the meaning of the word. The translation of the word merely as unique or only entirely loses the filial relationship it suggests. The word is never used and would never be used of an only uncle, aunt, brother, or sister, because it implies a unique relationship with one’s father.
(2) In one important occurrence the idea of derivation is immediately associated with monogeneis. John 1:14 asserts: “And the Word became flesh, and dwelt among us, and we saw His glory, glory as of the only begotten from the Father, full of grace and truth.”
(3) In the Nicene Creed the Greek fathers (who probably understood their Greek even better than modern scholars) associate monogeneis with and explain it by begetting: the only-begotten Son of God, begotten of the Father before all worlds light of light, very God of very God, begotten not made. Here monogeneis is translated only-begotten and then explained as involving being begotten and derived from the Father. It is hard to resist the notion that the Greek fathers understood monogeneis to mean only begotten and not merely only or unique. God’s Son is not merely unique. He is only begotten!