The text is the opening of Horace's eighth book of satires:

Olim truncus eram finculus, inutile lignum, cum faber, incertus scammum faceretne Priapum, maluit esse deum.

Once upon a time I was the trunk of a fig-tree, wood good for nothing, and the carpenter, uncertain whether to make of me a stool or a Priapus, decided I was to become a god.

The story is told in the first person by Priapus, or rather by the chunk of wood out of which a Priapus was carved, and set up in the orchards and fields to frighten off birds and thieves.