After Batman catches Barry in the "Bat Cave", Barry tried to prove his identity by getting his suit out from his ring, what comes out however is Zoom's Reverse Flash suit. Batman speculates that Zoom did this because he wanted Barry to know who was responsible for the altered timeline.
However, in the end, we find out it wasn't Zoom but Barry who broke the Time Barrier to save his mother. So then if Zoom didn't alter time, why did he leave his suit in Barry's ring?
As Zoom states when he confronts Barry:
Her hero. How noble. Oh, wait. You didn't stop JFK from getting assassinated... ...or made sure Hitler stayed in art school. You saved your mommy. You missed her. And in a supreme act of selfishness, shattered history like a rank amateur... ...turned the world into a living hell moments away from destruction. And I'm the villain?
I always took this to be why Thawne leaves his suit inside the ring. Because this time, Barry was the "villain" and so effectively he should dress the part with a Reverse Flash uniform. However I don't think this is outright stated in the movie, rather it's just a clue for Barry to realise that Thawne is involved somehow.
