Malakhim are different from humans in countless respects, ranging from their eternal youth to their elemental powers. Most importantly, malakhim do not exude malevolence, and this is why they tend to sequester themselves away from humans, aside from general distrust after what the Abbey has done to their kind.
Eizen is not like most malakhim. If anything, he exhibits characteristics that are more human than ethereal, and this sets him apart from most of his brethren. Even his sister claims that she despises humans (though this may be attributed to Eizen's fate in Zestiria's timeline).
Considering the state of relations between the malakhim and humans in Berseria's era, Eizen can be said to possess a bizarre preoccupation with the latter. For as many humans he dislikes, there are as many—if not more—whom he cares about. It's strange to behold an older being who has absorbed countless values and ideas from a supposedly lesser species, yet there's a clear reason as to why this is the case.
Prior to meeting Aifread, Eizen had suffered on a quest that he didn't know would succeed or not. Malakhim are a stagnant people; they live at large in solitude, and their unchanging appearance upon reaching their peak power emphasizes this fact. In comparison, humans age and change much faster. After Aifread's lecturing, Eizen was gifted with a new perspective and discovered a path that hadn't crossed his mind.
Eizen's admiration for short-lived creatures, including the rhinoceros beetle, speaks for his changed outlook on life. As a malak, he technically possesses immortality, but this means nothing to him if he doesn't pursue his love of exploration. By observing the resilience and zest of humans, Eizen learned that life offers endless possibilities, and that his once looming curse is not as big as he'd once thought. Through the eyes of humanity, he thus learned how to accept all of himself, as well as be more than the sum of his parts.