The line is actually a complete stanza in one of Machado's "Proverbios". His "proverbs" are pretty philosophical and enigmatic. There is no way to tell for sure what he meant by this. However, "todavia" can be a synonym for "siempre" (see e.g. RAE definition) and surely this was in Machado's mind when coming up with the line.
As this is for the intro to an art gallery catalogue, it seems likely that the author of the catalogue was thinking of time or contemporaneity when choosing the Machado quote (e.g. maybe a reference to the way specific instants captured by an artist have universal validity or else perhaps it is an exhibition of contemporary artists' work which engages with the subject of time or the canon). In any case, the phrase was also probably chosen because it's snappy and enigmatic. I think my suggestion captures these elements.
(Also: Deborah Lockett's interpretation of what the line means seems a very good guess to me)