
Covenant's act against Lena was like the mightiest of explosions at the entrance to these caves. The reverberations (consequences) have echoed, endlessly, through thousands of caves, through hundreds of miles of caves, the echoes passing into every last nook and cranny.
And the echoes have continued, for thousands of years into the future of the Land and it's world. There is no getting past them. The consequences, the aftermath, affects everything that is happening, sets a backdrop against which the characters must act.
That is why the hate versus forgiveness versus letting it go question is so relevant. The issue will not go away. Covenant and Linden have to continuously deal with it, or at least with it's aftereffects.
I don't think Stephen Donaldson is asking us, the readers, to forgive at all. I don't think he is asking us to take any particular stance.
What Stephen Donaldson is doing, is employing the consequences of that one terrible act as a major driving force in his epic story.
The reader is never allowed to forget that act. Ever. Period. Each new sunrise under the Sunbane is a reminder. Each day that Covenant steps closer to his doom in the Second Chronicles, is a reminder. Each time we think of the Staff of Law, is a reminder. Covenant's own thinking is modified and shaped heavily by that act. Linden is affected by Covenant. And on and on.