“And He is the radiance of His glory and the exact representation of His nature, and upholds all things by the word of His power...”
Hebrews 1:3 is not describing a lesser god, and it is not describing an exalted man who was absent until Bethlehem. It says the Son is ἀπαύγασμα τῆς δόξης καὶ χαρακτὴρ τῆς ὑποστάσεως αὐτοῦ - the radiance of God’s glory and the exact imprint of His being.
No creature can be that. Not a secondary deity whose nature is infinitely less than the Father’s, and not a later-exalted man who came into existence in time. If the Father’s being is eternal and infinite, an *exact* representation of that being is not a finite copy and is not a nature acquired after non-existence. Unless you abandon biblical monotheism, the text will not give you either construct.
The grammar tightens the point. The writer does not say the Son became the imprint - ὃς χαρακτὴρ ἐγένετο. He says ὃς ὢν… χαρακτήρ: who *is* that imprint. Ὢν and φέρων stand as His present condition. Ποιησάμενος and ἐκάθισεν mark completed acts in time: He made purification for sins and sat down. Identity first; then the saving work. The contrast in the verbs is hard to miss.
That does not mean a present participle magically proves eternity by itself. It means the writer grounds the Son’s saving work in who He already is, not in a nature He acquired, and not in a man who was not there in the pre-existence. Combined with the rest of the chapter - creatorship, immutability, eternality applied to the Son from Psalm 102 - the text leaves no room for a time when He was not the χαρακτήρ of the Father’s essence.
In every Unitarian and JW reading I have seen, the Son ends up *not* the exact representation of the Father’s being. He is close, exalted, unique - just not χαρακτὴρ τῆς ὑποστάσεως αὐτοῦ. If He is less than that, the christ on offer is NOT the one Hebrews describes. That christ cannot save.