The text of the spell says, "That entity sends a Celestial, an Elemental, or a Fiend loyal to it to aid you". It isn't just a bunch of Aether that you are forming into a creature like the summon monster spells (or even the conjure monster spells), you are getting an actual outsider that has probably seen and talked to the god (or at least a higher-level servant) [which is why I always encourage the party to talk to the ally to see if the god has any messages or useful information to impart], and now you have violated all kinds of laws of decency and hospitality and gratitude and thumbed your nose at the god (important in case it is an evil god that doesn't care about decency and hospitality, but you can be sure it cares about obedience and the money you are taking out of its pocket by tying up one of its "good earners").
