The phrase "wrong against it" refers to actions or behaviors that go against one's own nature or true self. Blake argues that what is considered right or wrong can vary from person to person, and what might be considered wrong by one person may be right for another. Each individual has their unique constitution and set of values, and what aligns with one person's nature may not be the same for someone else.
By asserting that the only true standard of right and wrong is what aligns with one's own nature, Blake challenges conventional moral frameworks and invites the reader to consider the subjective and relative nature of morality. He suggests that individuals should not blindly follow external moral codes but rather should look inward and find their own authentic sense of right and wrong, based on their own constitution.