A reader writes:
I was wondering about the origin on the custom of not leaving the
Exposed Eucharist alone during Adoration? Is it canonical law or what?
First, kudos for recognizing the distinction between adoration and exposition. One can adore the Eucharist whether exposition is taking place or not. Many folks get these two mixed up.
In inquiring about the origin of the rule, I take it that you are asking what is the basis for this in current ecclesiastical law, rather than its historical origin. If you are looking for information on that, you might try here.
The Code of Canon Law only deals briefly with the subject of Eucharistic exposition. Those canons are part of the general section on the reservation of the Eucharist, which are online here.
The actual basis for the requirement is found in the Church’s liturgical documents. Specifically, it is found in a document known as Holy Communion and the Worship of the Eucharist Outside of Mass, which is published in The Rites, volume 1.
The section on the exposition of the Blessed Sacrament explains:
85. If exposition of the blessed sacrament goes on for a day or
for several successive days, it should be interrupted during the celebration of Mass, unless it is
celebrated in a chapel separate from the area of exposition and at least some of the faithful remain
86. In churches and oratories where the eucharist is
reserved, it is recommended that solemn exposition of the blessed sacrament for an extended period
of time should take place once a year, even though this period is not strictly continuous. In this
way the local community may meditate on this mystery more deeply and adore.
This kind of exposition, however, may take place only if
there is assurance of the participation of a reasonable number of the faithful.
88. Where there cannot be uninterrupted exposition because
there is not a sufficient number of worshipers, it is permissible to replace the blessed
sacrament in the tabernacle at fixed hours that are announced ahead of time. But this may not be done more
than twice a day, for example, at and at
From what I can tell, there is not an explicit statement to the effect that "There must always be at least one of the faithful present in adoration during the exposition of the Eucharist" in either of the main legal documents that are relevant (i.e., the Code and the one I just quoted), but it seems implicit in Holy Communion and the Worship of the Eucharist Outside of Mass that there are to be people present in adoration during exposition. Otherwise there would be no point to talking about needing a sufficient number of people to allow for a lengthy exposition.
Still, one could read this and say, "Okay, so you need people there generally, but not necessarily every single moment. If someone needs to step out of the room for a few minutes for some important reason, that would be okay."
Given the way HCWEOM is written, you could take that interpretation if you were of a mind to.
Which is why God created instructions issued by Vatican dicasteries.
According to the instruction Redemptionis Sacramentum, issued by the Congregation for Divine Worship and the Discipline of the Sacraments,
[138.] Still, the Most Holy Sacrament, when exposed, must never be left unattended even for the briefest space of time. It should therefore be arranged that at least some of the faithful always be present at fixed times, even if they take alternating turns.
The instruction thus clarifies the ambiguity that one could see in the primary legal document.
So there you have it.