I remember my perplexity when I first encountered the doctrine of the Son’s eternal generation (i.e., being eternally begotten of the Father). I was preparing for seminary by reading Louis Berkhof’s classic Systematic Theology, and I found the topic overly speculative. I recognized the importance of affirming that the Son of God is not a creature but is Himself God. But I could not conceive why it was necessary to discuss the nature of the Son’s begetting in such detail. Where in the Bible would one get such an idea? And why does it matter?
It turns out that it matters a great deal and that it’s not as speculative as it may seem at first.
The God of Scripture is Trinitarian—one God in three persons. The distinctions between the persons are not between levels of deity, for all three persons are equally God. As the Westminster Shorter Catechism captures it, the Father, Son, and Holy Spirit are “the same in substance, equal in power and glory” (WSC 6). Christians should not doubt the deity or personality of any person of the Godhead. Instead, the distinctions among the persons of the Trinity are known as personal properties: the Father begets, the Son is begotten, and the Spirit proceeds from the Father and the Son. It is crucial that we understand these distinctions correctly, for denying them is the first step to many heresies. The Son is not somehow less divine than God the Father; the Son of God is Himself God no less than the Father is God.
So, to speak of the eternal generation of the Son is to speak of what is proper to the Son of God: He is begotten. This does not downplay the divinity of the Son in any way. The Son’s being begotten does not mean that His deity is less than His Father’s but means that He receives His personal subsistence from the Father. The divine essence itself is not begotten. Instead, in eternal generation the Father communicates the divine essence to the Son; Father and Son possess the same essence, without change.
And this generation must be eternal. The generation of the Son could not happen at a moment in time, for if it did, the Son would not be eternally the Son—nor would the Father be eternally the Father. If the Son’s generation were a singular event, this would mean that God in some sense changes. If the Father ever became the Father, or the Son ever became the Son, then God would not be immutable (that is, unchangeable). Because the Son of God never changes, His begetting must be an eternal begetting—it is not something that happened a long time ago or once-for-all. It is a timeless, placeless, changeless communication from the Father to the Son. Neither does eternal generation entail any division in God, as though the divine essence is divided between the three persons or is multiplied from one person to another. Each person possesses the same divine essence and the fullness of the divine essence. Eternal generation is also a necessary act, which means that it always is and could not be otherwise.