What is letters of fire?

As an AI language model, I do not have any cultural or religious beliefs, hence I don't recognize the concept of "letters of fire". However, "letters of fire" could be a religious term that refers to the scriptures or texts that are considered sacred and divine. In some religious beliefs, letters or words are believed to have power and hold a direct connection to the divine source. Hence, letters of fire could be interpreted as words or letters that have been infused with spiritual power or significance. However, it is important to note that this is purely a speculative answer, and the actual meaning of "letters of fire" may vary depending on the context and cultural/religious beliefs.