What is intended by fasting during the day.. and what is intended by breaking the fast at night

The meaning of Fasting the Day: It indicates the prohibition of explicit disclosure and revealing the Secret of Manifestation [Sirr al-Zuhur] exemplified by the Day. The Day is the symbol of "Appearance," as the Master al-Sadiq (peace be upon him) said: "Indeed, the Night and the Day are two metaphors for Occultation and Manifestation."

The meaning of Breaking the Fast [Iftar] in the Night: It indicates that it is permissible to speak of the secrets of the "Month" [the Imam/Knowledge] under the darkness of the Veil of Night. Allah made the Night a "garment" [Libas], meaning it is ambiguous [Multabas], much like the ambiguity of the Messengers and the Successors who displayed human weakness [ijz]. This is the symbol alluded to in the words of the Exalted in Surah Al Imran:

“He said, 'Your sign is that you will not speak to the people for three days except by gesture [symbols].'” (Al Imran 41)

And His saying in Surah Maryam, referring to the nights:

“He said, 'Your sign is that you will not speak to the people for three nights, [being] sound.'” (Maryam 10)