Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. The People of the Book. [Reported by ʿAṭāʾ al-Khurāsānī from Ibn ʿAbbās; also the view of Mujāhid]
2. It refers specifically to the Christians. [Al-Shaʿbī, al-Rabīʿ]
3. The followers of all (past) religions. [Reported by Abū Ṣāliḥ from Ibn ʿAbbās]

Who does "those who were before you" refer to?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. The comparison is in the rule and description of fasting, not in its quantity. Saʿīd ibn Jubayr states, "It was prescribed for them that if one slept before eating, it would not be permissible to eat until the next night, and marital relations were forbidden during the night of fasting. This remained obligatory upon them, while allowance was granted to you." According to this view, this verse is abrogated by the verse: "It is made lawful for you to go in unto your wives on the night of the fast." [Al-Baqarah: 187] The latter ayah introduced a distinction between the fasting of the People of the Book and the fasting of the Muslims.
2. The comparison is in the number of days. Within this, there are two views:
a. It was made obligatory upon this Ummah to fast three days of every month, and this was an obligation upon those before them. ʿAṭiyyah reports that Ibn ʿAbbās interpreted "As it was prescribed for those before you", saying: "It was three days of every month, then it was abrogated by Ramadan." Maʿmar reports that Qatādah said, "Before Ramadan (became obligatory), Allah had prescribed for the people to fast three days of every month." According to this view, the verse was abrogated by the verse "The month of Ramadan in which was revealed the Qurʾān..." [Al-Baqarah: 185]
b. It was prescribed for those before us to fast Ramadan itself. Ibn ʿAbbās states, "The Christians, however, would advance a day, then another, and then they would add a day. Then they said, "we will advance (the beginning by) ten days and delay (the end by) ten days." Al-Suddī reports from his teachers that the Christians found it difficult to fast Ramadan as it moved through summer and winter, so they agreed to fix a time for fasting between summer and winter, and they said, "We will increase twenty days as an expiation for what we have done (in changing the timing of the fast)." Based on this interpretation, the verse is definitive and has not been abrogated.

In what way does fasting for this nation resemble earlier fasting?