Because you can't act without the avatar. You might think you can, but in truth, Reul was useless against Ridire and his pet. That's why they call upon someone to act on their behalf.

[He says these words after a beat. Everything is becoming clearer.]

So, if you go without your avatar, you give up something. You may have entered a pact by arriving here that you didn't realize you stepped into, Loki.