Eternal generation of the Son

In what sense is the eternal generation of the Son a biblical doctrine?

Nazianzen's proposal, in his Oration 29, of the Son as begotten fromt the Father is derived from philosophical analysis rather than biblical exegisis. However there are biblical verses that could support His claims. For instance, he says the Son being begotten "from" the Father is not the same as the Son being begotten "after' the Father. This understanding avoids temporal words supporting the eternality of all persons in the Trinity. In John 16:28, Jesus affirms that he came forth from the father and will go to the Father. Likewise, John 1:18 uses the phrase "the only begotten Son" to refer to Jesus.s