Once you remove someone from your Block List, this person is again able to view your profile and contact you within the restrictions of your privacy settings.
If you were friends before the blocking, this connection will not be restored unless a new friend request is accepted.
Also keep in mind that, during the next 48 hours after you unblock someone, you will not be able to block this person again.
Related article:
How to Use Facebook >> Friends and Users >> What happens when you unblock someone on Facebook?
