1)
Why does it say "Tamar Kalaso"?
1.
'Rashi': This is astounding. Why did the Sefer mention something lowly about David's ancestor 1 ?!
1
I.e. that she bore children to her father-in-law.
2)
Why does it say "Kol Bnei Yehudah Chamishah"?
1.
Malbim: The Sefer mentions only the most outstanding children. One might have thought that Yehudah had more children who were less esteemed - the verse teaches that this is not so. Also, it teaches that Er and Onan came back to the world via Gilgul in Peretz and Zerach, via the Yibum, so all five were in the world.
