Excerpt
…“As is well known this famous expression “
subsistit in” was subsequently the object of many and contradictory interpretations. The notion became quite widespread that the Council had not wanted to adopt as its own the traditional statement according in which the Church of Christ is (
est) the Catholic Church — as was stated in the preparatory schema2 — so as to be able to say that the Church of Christ subsists also in Christian communities separated from Rome.
In reality, however, an analysis of the Council proceedings leads to the conclusion that
“[t]he phrase
subsistit in is intended not only to reconfirm the meaning of the term
est, that is, the identity of the Church of Christ with the Catholic Church. Above all, it reaffirms that the Church of Christ, imbued with the fullness of all the means instituted by Christ, perdures (continues, remains) forever in the Catholic Church”.3
This meaning of the term
subsistit coincides with the common language of Western culture and is consistent with classical philosophical language from Aristotle to St. Thomas; that which exists in itself and not in something else is said to subsist.4
“
Subsisting is a special case of
being. It is being in the form of a subject standing on its own. This is the issue here. The Council wants to tell us that the Church of Jesus Christ as a concrete subject in the present world can be encountered in the Catholic Church. This can occur only once and the notion that
subsistit could be multiplied misses precisely what was intended. With the word
subsistit, the Council wanted to express the singularity and non-multiplicability of the Catholic Church”.5
In this Document of the Council, the assertion of the subsistence of the Church of Christ in the Catholic Church is followed by the famous phrase about the presence of many elements of sanctification and truth, belonging to the Church, outside her visible structure.
The Congregation for the Doctrine of the Faith, already in 1985, in the face of erroneous interpretations, made the following statement in this regard: " . . . the Council chose the word
subsistit precisely in order to make it clear that there exists a single ‘subsistence’ of the true Church, while outside her visible structure only
elementa ecclesiae exist, which — as elements of the Church — tend and lead toward the Catholic Church”.6
More recently, the same Congregation declared: “The interpretation of those who would derive from the formula
subsistit in the thesis that the one Church of Christ could subsist also in non-Catholic churches and ecclesial communities is therefore contrary to the authentic meaning of
Lumen Gentium”.7"…
https://www.ewtn.com/library/Doctrine/subsistit.htm