Halocho #1323 - Why do the firstborns fast?

Why don't firstborns celebrate the fact that they were saved from the 10th plague - the smiting of Egyptian firstborns?

On Erev Pessach - this coming Monday - all firstborns will fast in memory of them fasting in Egypt on Erev Pessach, to ensure they wouldn't be punished along with the Egyptians in the 10th plague.

The Hallel said at the Seder includes praise for their delivery.

All firstborn males fast; even if they're only a firstborn to one of their parents.

Even firstborns who are exempt from Pidyon haBen - like Cohanim, Levites or being born after a stillborn - also have to fast.

The father of a young firstborn needs to fast for him.

Whether a firstborn (or his father) may attend a Se'udat Mitzva like a Siyum, Brit or Pidyon haBen and break his fast to participate in the meal, depends on local / family custom.

After breaking his fast, he can eat the rest of the day.

Source: Kitzur Shulchan Aruch 113:6, 115:2

- Danny
Tuesday, 8 Nissan 5770

Please daven for 3 year old נָעֳמִי בַּת דִינָה who is being treated for lymphoma