The Greek eisagō means to bring or lead into. It appears in Luke 2:27 when Simeon came into the temple as the parents 'brought in the child Jesus' (eisagagon) to fulfill the purification rites. It also appears in Acts 21:28-29 in the false accusation that Paul had 'brought Greeks into the temple.' In Hebrews 1:6, God the Father 'brings his firstborn into the world' — a declaration of the Son's royal entrance into creation.
Hebrews 1:6 uses eisagō for the Father's act of introducing the Son into the world: the Incarnation seen from heaven's throne room — not a birth in obscurity but a royal presentation. The angels are commanded to worship. Eisagō frames the Nativity as an audience with the cosmos: the Son is led in, and all of heaven bows. The manger's humility did not diminish the throne-room reality.