What will he call?
Malbim: His second mission is to herald reward for Tzadikim and punishment for Resha'im.
What is "Shenas Ratzon"?
Rashi: It is a year of appeasement.
Radak: It is a year of redemption - "u'Virtzoni Richamtich" (60:10). The years of Galus were of anger -"b'Katzpi Hikisich" (ibid).
Malbim: This is Midas ha'Rachamim. Hashem will be pleased with His nation to pay their reward. It will be an entire year, as opposed to Yom Nakam (refer to 61:2:3:2).
What is "Yom Nakam"?
Radak: It is the day of Gog and Magog. Hashem will take vengeance on them. Via this, he will console all the mourners. Afterwards, it explains who are the mourners - "la'Avelei Tziyon" (3).
Malbim: This is Midas ha'Din to take vengeance on Nochrim. They will fall in one day. The same applies below (63:4).