ἀπάτωρ ἀμήτωρ ἀγενεαλόγητος, μήτε ἀρχὴν ἡμερῶν μήτε ζωῆς τέλος ἔχων, ἀφωμοιωμένος δὲ τῷ υἱῷ τοῦ θεοῦ, μένει ἱερεὺς εἰς τὸ διηνεκές.First, note the staccato opening: three alpha-privatives, no conjunctions: ἀπάτωρ ἀμήτωρ ἀγενεαλόγητος.
Then note the suspended present participle ("neither beginning of days nor of life an end having"), followed immediately by a perfect passive participle (ἔχων, ἀφωμοιωμένος), then the point: Christ remains a priest for perpetuity.
One last note, and this an interpretive/theological one: if Melchizedek was ἀφωμοιωμένος δὲ τῷ υἱῷ τοῦ θεοῦ, then he wasn't likely himself ὁ υἱὸς τοῦ θεοῦ, was he? That is, one is not made like what one is. This should effectively rule out the suppositions one occasionally hears that Melchizedek was a pre-incarnational Christophany. The Son of God is not made like the Son of God.