Who are the "Anavim"?
Rashi: They are the patient, who bore Hashem's yoke and decrees.
Malbim: They are Tzadikim; refer to 29:19:2:2.
Why does it say "v'Yasfu Anavim ba'Shem Simchah"?
Radak: They [who did not heed the Navi's rebuke] will be afflicted, and the humble will increase to rejoice in Hashem. They believed in him before the affliction. They will rejoice more when they see that the Nevu'ah is fulfilled - affliction for Resha'im, and relief and honor for the humble.
Malbim: Shem Hashem alludes to the Creator, who conducts the world with nature. "Kedosh Yisrael" hints to His Hashgachah Pratis, signs and wonders. Simchah is constant; Gil is [joy over] a new matter. Anavim are Tzadikim; Evyonei Adam are commoners. Tzadikim and Anavim do not need supernatural miracles. They believe in Hashem because he created the world and conducts it constantly. Like they rejoice, they will continue to rejoice in His conduct. Evyonei Adam did not rejoice in Him, for they did not recognize Him. They will have new joy via Kedosh Yisrael - the miracle that will be done then.
Who are "Evyonei Adam"?
Radak: They are the humble in Yerushalayim; The matter is repeated in different words.
Malbim: They are commoners; refer to 29:19:2:2.
