1)
What is the meaning of "b'Ein Chazon Yipara Am"?
1.
Rashi: When Yisrael cause Nevu'ah to depart from them, via insulting the Nevi'im, breaches come in them, and they go to evil conduct.
2.
Malbim: When the last Navi (Mal'achi) completed his Nevu'ah, he said "Hine Anochi Shole'ach Lachem Es Eliyahu ha'Navi", "Zichru Toras Moshe Avdi" (Mal'achi 3:23, 22). As long as there were Nevi'im, they were Hashem's messengers to straighten the nation. When the visions were sealed, they need to remember the Torah (they are prone to be unruly).
2)
Why does it say "v'Shomer Torah Ashrehu"?
1.
Malbim: He will attain happiness via guarding Torah. It will stand in place of Nevu'ah.
