For most of the Iliad, we see less compassion and forgiveness than their opposites. For example, when Achilleus rejects the gifts Agamemnon is offering him to come back to the battle, he both refuses to forgive Agamemnon and displays no compassion for his fellow Achaians, who are getting slaughtered by the Trojans. Things get even worse later on, when we see him killing guys who are trying to surrender (Agamemnon and Menelaos do the same thing in Book 6), and when he refuses to make any deal with Hektor, his enemy. But just because we don't see any compassion and forgiveness doesn't mean that the theme isn't there. You could even say that these ideas become all the more important the more we see them violated. If you don't believe us, take a look at the end of the poem, when all of a sudden we get tons of compassion and forgiveness, almost as if that's what the story's been waiting for. Coincidence? You be the judge.
Compassion and forgiveness are the most important themes in the Iliad.
Anger is the main obstacle to compassion and forgiveness in the Iliad.