To call the Son God but then affirm that he does not share the nature of the Father equivocates on the most basic level. The Son is not both God and not God at the same time. He shares in the Father’s nature fully. That is why he is God. And for no other reason.
A few years ago, a number of prominent pastors called the eternal functional subordination view (EFS) outside of the bounds of orthodoxy. Some saw such attacks as imputing heresy to EFS. And one recent book considers EFS in the same orbit as Homoianism, a particular strand of Arianism (the denial that the Son shares the same divine essence as the Father).
It is worth, then, reviewing Gregory of Nyssa’s response to Eunomius, a so-called Anomoean who could call the Son “God” while also affirming that the Father is greater than the Son. It is worth doing so because many of us repeat the same arguments as Eunomius but with orthodox conclusions.
Eunomius, a so-called Anomoean could call the Son “God” while also affirming that the Father is greater than the Son. Gregory of Nyssa (and his brother Basil) knew that this was theological gibberish. If the Son is less than the Father and does not share the nature of the Father (as Eunomius claimed), then “God” is a worthless nickname.
They were right. Words matter. It matters how we talk about God.