What he said: I, Loki, Prince of Asgard, Odin’s Son, the Rightful King of Jotunheim, God of Mischief, do hereby pledge to you my undying fidelity
What it meant: I, Loki, Stepping-stone of Thor, Odin’s Scapegoat, the Dispensable Plot Device of the MCU, God of Knives, do hereby give my life up to fuel Thor’s Manpain™, for the sake of furthering his storyline and character development, or so the Russos claim; and also to sacrifice myself (again) for my brother as a form of “redemption” due to the writers’ laziness and lack of creativity, even though I already did that before in The Dark World, but it was retconned into a “faked death” and a joke in the eyes of the audience thanks to the irresponsible writing in Gagnarok.
Just to clarify, I have nothing against the characters.