Classical Mandaic, written in these letters, is a liturgical language. It has a living descendant, usually called Neo-Mandaic, spoken by a very small number of people, and the relationship between the two is close without being identity: the classical language is preserved by the texts and the spoken one has gone its own way, as the weakening of the gutturals shows.
The number of speakers is very small and the community that carries the language is small too. Mandaeans are a Gnostic religious community of southern Iraq and south-western Iran, the only ancient Gnostic tradition with a continuous living membership, and since the early years of this century violence and displacement have scattered much of it into a diaspora spread across several continents. A liturgical script survives dispersal better than a spoken language does, because the books travel and the daily conversation does not.
That is the context in which a page like this one should be read. This is not a historical alphabet being described from the outside for interest. It is in current use by people, and the language behind it is endangered in the specific sense that linguists use the word.
What the atlas records about the letters is what can be stated publicly and checked. What the letters mean inside the tradition is the priesthood's, and it is not set out here.