This plugin automates setting up 1-to-1 mapping between Blogger.com (blogspot) blog posts and your new WordPress blog posts.
If you have imported posts from Blogger.com (blogspot.com) then you might be redirecting visitors from your blog to homepage of your new WordPress blog. Which is wrong, as a user may feel lost when we lands up on your homepage unexpectedly.
This plugin handles traffic redirection part in a way that visitors will see be redirected from old Blogger.com post to same post on new WordPress.com blog on 1-to-1 basis.
You can find detailed instructions to use this with screenshots here.
Link - Installation & Setup Guide