The poem describes pushing open the gate of heaven and entering the palace of the Emperor of Heaven.
Tips
history
阊 is not used alone. It survives in 阊阖 ('the gate of heaven', also a poetic name for the west wind) and the Suzhou city gate 阊门. The gate radical 门 gives the door meaning; 昌 supplies the sound.
register
Literary and archaic. You meet 阊 only in classical poetry, the fixed word 阊阖, and old place names.