User blog comment:The Milkman/Indoctrination Theorists Say the Darndest Things, Part II/@comment-98.240.62.123-20121205183510/@comment-5830255-20121205201632

Arrival isn't outright necessary for Indoctrination, it however gives insight to the player and Shepard. If you hear "Your mind will be mine" it gets quite suggestive if you know what I mean.