This antiphon Aperite mihi portas set by Giovanni Dragoni is a very short antiphon sung at the end of the in exsequiis Defuncti, the burial services at the graveyard.
If we oversee the literature some different theories are there at what moment this short Antiphon was implemented in the Office of the Dead.
Considering the actual entombment it is very difficult to keep the Roman and Galician traditions in that time sorted out from each other in the available sources. Nevertheless the antiphon Aperite mihi portas, was a fixed value in the former last burial services which was however sung according to the one source at the gate of the graveyard, according to other whereas the priest prays standing before the grave and according to a third one during the entombment itself.
To our opinion the most probably the aperite mihi portas was sung after the last Requiescant in pace on the graveyard, at the end of the in exsequiis Defuncti at the moment the body was buried/delivered into the grave under singing the Gregorian antiphon, plainchant Aperite mihi portas followed by the psalm Confitemini (p. 117).
In the Plainchant modus this Antiphon has a duration of about 3’25”.
This Aperite mihi portas is set for four equal voices TTBB and is fully written in sober homophonic style, example of clarity of declamation of the words, contrary to the setting of Givovanni Francesco Anerio (1567-1630, see there. This setting by Dragoni has 14 bars and has some severe modulations but only some minor rhythmic changes.
It ends in a hopeful A-major hoping or stating the justified shall enter the gate of the Lord.
The text of the Antiphon is among others found in Monza, Chapter Library cod. c. 12.75. The Monza Antiphoner. Source M of R.-J. Hesbert, Corpus Antiphonalium Officii.
Text:
Aperite mihi portas justitiæ: ingressus in eas confitebor Domino.
Hæc porta Domini : justi intrabunt in eam.
Translation:
Open to me the gates of justice: I will go in to them, and give praise to the Lord.
This is the gate of the Lord: the justified shall enter into it.