Dean as Cas’s Lily
Let’s recap the Isham and Lily story.
Lily summons him, not knowing what sort of power or presence she accidentally brought on to the earth. She clearly revered and adored him and he, in turn, gave her all the angels super secret secrets because he fell in love with her. She say him as nothing more than an Angel, a holy being she worshiped. She had no other interest in him, and slowly started getting uncomfortable with his demands. Luckily, she knew enough now to summon a guardian angel (and I believe that was all Akobel was, but consider the times- a man and woman could not live together without the pretense of marriage)
I don’t know how Akobel managed to hide her, but he did. Isham, enraged, sought them till he found them, killed Akobel out of nothing more than jealous rage. According to Isham, he’s blameless. He believes that he’s ‘given’ Lily the information she sought, and he loves her, so she now ‘owes’ him her body and heart. Very rapist-like, ugh. And because she refuses, because she still resists, he kills May.
And all the barbs Isham throws at Dean and Sam- that all humans lie, they’re filthy, they’re harmful to angels.. very similar to what some men say about women being sluts or cockteases, just because they won’t put out.
Back to present day.
Think about it. Isham openly saying he envied Castiel- for surviving hell, for being God’s chosen. Cas survived hell for Dean. Cas was the one who saved the Righteous Man, and clearly that was a tremendous honor. Cas, who was once below Isham, yet seemed to have been the only one to rise in the ranks… While Isham and company stayed where they were.
So there’s some amount of professional jealousy involved.. and a lot of the personal.
Cas rescued Dean from hell, they fought together for years. All of the angels know this. Now when Isham first sees Dean, the human has just barged into the diner FIVE minutes after Cas because he was worried. And he proceeds to just sit there and sass Isham right back. He doesn’t care that Isham is far more powerful than him. He just sits there, nestling close to Cas, arms out and on the table. And in front of Isham, they present a united front.
Even later, when Cas is about recount the story, Isham stops him and proceeds to insult Dean and Sam. Cas refuses to listen, he treats Dean and Sam like equals and friends. And they reciprocate by trying to talk to Lily, putting themselves in harm’s way for Cas.
When asked to chose between Dean, a mud monkey, and his brother, Cas chooses Dean without hesitation. This is the final straw for Isham who proceeds to say this interesting bit-
I couldn’t have the human I loved and desired, so you can’t have the one you love and desire either!
Only Dean’s prepared to blow him away. So Isham tries to use Dean’s love for Cas, knowing deep inside that it’ll work. And it does.
Dean won’t roll the dice. He’s willing to die for Cas.
Cas has this human’s love without even trying.
Cas didn’t have to tell Dean all of heaven’s secrets or threaten or bully Dean into loving him. Dean just loves him.
Can you imagine how galling that must be to Isham?