Blocklisting is intended to hide messages from you that you're not interested in, for example spam messages, people who are harassing you that you want to ignore, etc. Blocklisted people don't receive anything when they send you a text message, from their point of view, they wouldn't even know that they're blocklisted.

Just long-hold any contact in the conversation list, and press "Blocklist".

To Unblocklist a contact.

To remove a contact from your blocklist, go to the Chomp SMS > Settings > Security and Blocklisting > tap on the contact you'd like to unblocklist.

This contact and their messages will now show in your Chomp SMS conversation list screen, as expected.