"The Son exists because the Father exists: but there never was a time before the Father produced the Son."

Lewis may have in mind the opening passage of John 1, which uses the phrase "the Word" to refer to Jesus Christ: "In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God" (John 1:1-2, ESV).

Lewis speaks further about Christ as "the Word" when he says, "He is the self-expression of the Father--what the Father has to say" (pp. 173-74).