Hudson Taylor tells the story of the agonizing leaving of his mother at the dock on his first missionary trip to China. Composed till the last moment, she at the last let out a shriek of agony embodying the motherly loss she felt at the sacrifice of her son for the cause of missions in China. Taylor remarks that it was in that moment that she understood better than ever before the great sacrifice proclaimed in the gospel.
This is the pinnacle of the argument for the eternal generation of the Son of God.
Deny this doctrine—deny eternal sonship—and you empty the gospel of no small part of its glory. Think for a moment of how the biblical statements the love that was resident in the Father sacrificing His Son for us.
John 3:16 For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.
Romans 8:32 He who did not spare His own Son, but delivered Him over for us all, how will He not also with Him freely give us all things?
1 John 4:9-10 By this the love of God was manifested in us, that God has sent His only begotten Son into the world so that we might live through Him. In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins.
Samuel Miller remarks: “In all these passages, it seems to be implied, if I can construe language, not only that the Father had a Son, before he was sent, who was infinitely beloved, but that in the original counsel and determination to send this glorious Personage to be the Savior of sinners, there was a real and immeasurable exercise, if I may so speak, of paternal feeling, put to an unparalleled test, and exercised to an extent incomprehensible to creatures.” Miller proceeds to argue that this emphasis of Scripture is deceptive and empty, unless the Son was a genuine Son to the Father when He was given. Eternal generation provides the basis in the Trinity for this genuine sonship and the paternal love of the Father for the Son. Without eternal generation this love is ungrounded and unexplained.
What happens to this love if the eternal father-son relationship in the Trinity is denied? If it is simply one arbitrary person giving another arbitrarily chosen person because of an artificial covenantal arrangement, what becomes of the pathos of a Father giving His Son for our salvation? It is destroyed and with it much of the glory of the gospel! What is ultimately at stake in the doctrine of the eternal generation of the Son is one of the glories of the gospel!