Almost every verb has a noun that implies "the act and effect of" whatever the verb is. So, an existence is the act of existing. Nonetheless, the most simple verb, to be seems to lack such a noun, at least in Spanish (link in Spanish, sorry).
But then someone came up with essence as a possibility for the noun of to be, but in Spanish it lacks that meaning (it means roughly "the most important and charasteristic part of a thing"). But what about Latin? In Latin we have exsistĕre and its noun exsistentia, and also essentĭa which seems to mean the being or essence of a thing, according to the Lewis & Short dictionary.
Can then essentĭa be understood as "the act of being" the same way as exsistentia is "the act of existing"?