Ahh, well I said her memories were very strong right? They held great magic and by making her collect them, he could in turn collect the magic. He wanted her abilities and all the magic of time in order to become more powerful then anyone else. But he wanted to do things with that power that people should never be allowed to do. The wizard was a very very bad man and he didn't care at all for other people's feelings. And feelings can hold the most powerful magic of all.