What is the meaning of "Zarach ba'Choshech Ohr"?
Rashi: This is like Hizri'ach (Hashem will make light for them amidst the darkness).
Rashi (from Shocher Tov 27:1): Hashem Himself will illuminate for them - "Hashem Ori v'Yish'i" (27:1).
Radak #1: At a time of darkness in the world, i.e. affliction, Hashem will make light for the straight - relief. Zarach is Po'el Yotzei (it acts on others; He makes light shine).
Radak #2: Zarach is Po'el Omed (the action applies only to the subject). Chanun v'Rachum refers to a person who learned from His Creator's Midos.
Malbim: Also amidst darkness, when the light of success is darkened, and he is afflicted in this world, Hashem will make light shine for him.
Why does it say "Chanun v'Rachum v'Tzadik"?
Radak #1: In His ways he is gracious, and has grace on good people. He is merciful, and saves them from affliction. He is Tzadik and straight, and gives to the good according to their ways, and to the evil according to their deeds.
Radak #2: Refer to 112:4:1:4.
Malbim: Hashem brought the darkness for the person's benefit and the salvation of his soul. Either it is due to Chaninah, to increase his reward, or mercy, to cleanse his sins, or due to Tzedek - to receive the punishment for a sin that he did.
