Question: Gemara cites three examples of "Halacha Pesuka". Why are those particular ones cited? What do they have in common?
All of these Halachos come from areas of Halachah that involve very complex discussions. These Halachos, though, completely avoid the complexity of those areas.
(a) Seeing blood the size of a mustard seed. Jewish women are strict no
matter how much blood they see, and they do not make their status dependent
on the requirements of the letter of the law (which, in the laws of Nidah,
is very complex).
(b) Avoiding the obligation of Ma'aser. Through the method mentioned in the
Gemara, one avoids the complex Halachos that may arise if one has a doubt
whether he tithed his fruits.
(c) The blood that comes from an animal when bloodletting has Me'ilah.
Blood that came from an animal during Shechitah does not have Me'ilah.
The source for this is complex, and this law itself is somewhat
counterintuitive. Blood that came from an animal during bloodletting has
Me'ilah -- this is a simple, straightforward Halachah that avoids the
complexity of the law of blood that came during Shechitah.
Shabbat Shalom,
M. Kornfeld
It was suggested in our Shiur (Ner Yisrael, London) that these three Halachos were selected because they relate to the three cardinal sins and also "Al Shlosha Devarim Ha-Olam Omed - Torah Avoda & Gemilut Chassadim".
Therefore the GEmara uses these as examples for Halchot which can never be
disputed.
Shabbat Shalom
Danny Wulwick from London
Alan Schoffman askes about the three examples of Halacha Pesuka. I suggest he looks at the Shlo Hakodosh in Snei Luchos Habris on Tomid chapter 13, at the end. In the Oz Vehodor edition of the Shlo it is on page 316, were he connects all three examples to different aspects of davening. It is worth while looking there for a good explanation.
Good Voch.
David Leitner, Manchester