Yes, It is very possible to block someone to comment or make posts on your wall without affecting your activities with them on Facebook messenger. Facebook also enables you to set your privacy either by making your post public for everyone or making your posts visible to only your friends or making your post private to only you.
You can actually block anyone on Facebook to prevent them from making post on your wall provided such person is your friend on Facebook. If the person get blocked by you, such person will never see your posts any longer but it doesn't affect your interaction with Facebook messenger. You can also decide to block the person on Facebook messenger if you wish just like you blocked the person on Facebook.
Also, you can also unblock anyone you've blocked on your Facebook account if you wish. The fact is that you are the owner of your account and you control what happens. You also decide those whom you wish to be part of your friends or see your posts or even make posts on your account because you are the owner of your account.
Thanks for reading and I hope this helps.