Lincoln grasped something that escapes most people in conflict: that enmity isn't a fact of nature but a *choice* we make repeatedly, and therefore a choice we can refuse. The repetition—"we must not be"—suggests this isn't sentimental wishfulness but a discipline, perhaps even a warning to himself about the seductive certainty that comes from hating. When you're in a bitter divorce or estranged from a family member, this matters: you're not bound by what happened yesterday; you can decide today whether to crystallize the hurt into permanent opposition, or keep the door to reconciliation from closing entirely.