Scripture-first response
“The Son had glory before the world existed.”
Scripture can speak of realities prepared in God’s purpose before creation. The praying Son asks for the messianic glory purposed before the world to be realized after His work.
What the objection is claiming
Purposed or proleptic glory is assumed to require the Son’s separate personal existence before incarnation.
John 17:5
And now, O Father, glorify thou me with thine own self with the glory which I had with thee before the world was.Open full referenceJesus prays for the glory purposed for the Messiah before creation to be realized after His saving work.
How the passages answer it
The Son who prays is the real Messiah nearing the completion of His mission. Luke ties Sonship to the holy child’s conception, while John locates eternal preexistence in the Word that was God. The glory is rooted in God’s eternal purpose and revealed in the incarnate Son.