Why is a person who refuses to forgive another considered a sinner?

Question

The Rambam Hilchos Teshuvah 2:9 writes about what to do when asking for forgiveness from a person who won't grant it:

אֲפִלּוּ לֹא הִקְנִיט אֶת חֲבֵרוֹ אֶלָּא בִּדְבָרִים צָרִיךְ לְפַיְּסוֹ וְלִפְגֹּעַ בּוֹ עַד שֶׁיִּמְחל לוֹ. לֹא רָצָה חֲבֵרוֹ לִמְחל לוֹ מֵבִיא לוֹ שׁוּרָה שֶׁל שְׁלֹשָׁה בְּנֵי אָדָם מֵרֵעָיו וּפוֹגְעִין בּוֹ וּמְבַקְּשִׁין מִמֶּנּוּ. לֹא נִתְרַצָּה לָהֶן מֵבִיא לוֹ שְׁנִיָּה וּשְׁלִישִׁית.לֹא רָצָה מְנִיחוֹ וְהוֹלֵךְ לוֹ וְזֶה שֶׁלֹּא מָחַל הוּא הַחוֹטֵא

Even if a person only upset his friend by saying certain things, he must appease him and repeatedly approach him until his friend forgives him.

• a) If the wronged person doesn't want to forgive him, the person asking for forgiveness should bring a group of three friends and approach him with them and request forgiveness.
• b) If the wronged person is not appeased, the person asking for forgiveness should repeat the process a second and third time.
• c) If the wronged person still does not grant forgiveness, the person asking to be forgiven need not pursue the matter any further and on the contrary, now the person who refuses to grant forgiveness is the one considered as the sinner.

Two questions:

1) Why is the aggrieved party obligated to forgive the person who offended him, so much so that if he doesn't accept the 3rd apology he himself called a sinner? Maybe he was incredibly hurt!

2) The Rambam says that after the 3rd apology:

"the person asking to be forgiven need not pursue the matter any further"

Does this mean that even though his friend refuses to forgive him, Hashem forgives him anyway?

Answer 1

The sin in not forgiving is refusing to act the way God does. The summary of God’s 13 attributes is that God is merciful. This is why this passage is repeated many times in the Yom Kippur liturgy. The Talmud says:

All who act mercifully [that is, forgivingly] toward their fellow creatures will be treated mercifully by Heaven, and all who do not act mercifully toward their fellow creatures will not be treated mercifully by Heaven. [Shabbat 151b; also RH 17a; Meg. 28a]

The doctrine of “Imitation of God” states that we must emulate God’s 13 attributes. The Talmud says:

[God]…showed Moses the order of prayer. He said to him: Whenever Israel sin, let them carry out this service before Me and I will forgive them. [Rosh HaShanah 17b]

Commentators note that God does not say “SAY” these words and I will forgive you, (Yomru kaseder hazeh); but “FULFILL” these words and I will forgive you (Ya'asu kaseder hazeh). This is interpreted to mean: If you want God’s forgiveness, become more forgiving yourself. Likewise, Rav Nahman of Breslov said:

If you imitate God by being compassionate and forgiving, He will in turn have compassion on you, and pardon your offenses.