Why didn’t Rand immediately find Mat and put him in charge of the armies?
Rand knew where Mat was (the visions.) Therefore, he knew that Mat was with the Seanchan—so in going to find them, and bring them into the battle, he was doing just that. (To an extent.) Also, he understands that with Mat—unlike Perrin—swooping in and ordering him about is a good way to get Mat going the opposite direction. However, Mat also finds his way to where he needs to be. So, Rand decided to let the Pattern work on Mat, and instead focused on preparing Perrin .
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