Lyric discussion by A.M 

Cover art for English Fire lyrics by Cradle of Filth

It's more focused on the glory of the old ways IMO. England was before rome came, a pagan isle, along with Ireland etc.

"Now the tidal are turning Churning in darkness The celebrations of extinguished wars Are but stills in time"

That says that the status quo is changing, which could be paganism and christianity, the celebration of rome's victory over england is forgotten and the old ways are overtaking christianity.

And yes, the four fire festivals are about changing seasons, but also have certain deities attributed with them and themes. Imbolg is spring and sacred to Brighid, Beltaine is the sabbat of fertility and sexuality, Lughnasadh is the first and main harvest festival and Samhain is the festival of the dead and the brand new year according to Celtic Lore.