When cast on a dead humanoid you imbue the dead with the ability to complete its final testament. The target has 25 words to which it can make its final statement. This could either be what it was thinking in its last moments, a confession, a goodbye, an omen or something similar. The target of the spell is not able to converse with the living to answer questions but it is aware of their presence.

The spell doesn't return the creature's soul to its body, only animating its spirit. Thus the corpse cannot learn new information, nor does it comprehend anything that has happened since its death. Once the target speaks its message it disappears in a luminant glow, grasping shadow, flutter of fey butterflies or something similar depending on its alignment and beliefs/character. At Higher Levels the PC's soul is able to linger for longer, allowing 5 extra words per level of the spell after 1st level.

If the soul is unwilling, or has been trapped by any means, the spell fails.