Before you have surgery, you'd better give your consent, because the surgeon can't get his scalpel anywhere near your skin without first getting this permission from you.
Consent is permission that can be given or taken away. A father might give his consent to allow a young man to marry his daughter, but he might refuse that consent if he learns that the prospective groom has a prison record. A homeowner who won't give a developer consent to tear down her house and build a shopping mall might finally consent after receiving a very large check from the developer.