Aaron Gillespie has posted an update to his tumblr blog explaining some of his reasons for leaving Underoath after more than a decade:

When I was fourteen i was asked to join a band called Underoath this was long before any of the members you know now were here. We began as a sort of progressive-metalish type band. I just knew i was young and had an incredible opportunity to play as fast as i could, which was super fun. Fast forward- all the rad dudes you know and love joined this band and we made music together, and I believe with my all that God used it (and still does and will) to touch a lot of people. I feel so blessed to have been a part of this, it has been triple what i ever imagined or thought could happen,and some of the most fun times of my life.

Truth be told, things change, people change, lives rearrange. My time here in this band is up. I love it, the people, the traveling. It is just time for me to go.