Someone who lies on purpose is impious because they commit injustice. But someone who lies without meaning to is also impious. They go against the nature of the universe. They fight against the world's natural order. Anyone who goes against their own nature and works against truth is basically fighting a war against reality. Nature gave us the instincts and chances we need to find truth. If we ignore these gifts, we lose the ability to tell what is false from what is true.
He therefore that willingly and wittingly doth lie, is impious in that he doth receive, and so commit injustice: but he that against his will, in that he disagreeth from the nature of the universe, and in that striving with the nature of the world he doth in his particular, violate the general order of the world. For he doth no better than strive and war against it, who contrary to his own nature applieth himself to that which is contrary to truth. For nature had before furnished him with instincts and opportunities sufficient for the attainment of it; which he having hitherto neglected, is not now able to discern that which is false from that which is true.