Lying stands on a different plane from all other moral offenses, not because it is intrinsically more heinous or less heinous, but simply because it is the only one that may be accurately measured.
Forgetting unwitting error, which has nothing to do with morals, a statement is either true or not true. This is a simple distinction and relatively easy to establish. But when one comes to other derelictions the thing grows more complicated. The line between stealing and not stealing is beautifully vague; whether or not one has crossed it is not determined by the objective act, but by such delicate things as motive and purpose. So again, with assault, sex offenses, and even murder; there may be surrounding circumstances which greatly condition the moral quality of the actual act. But lying is specific, exact, scientific. Its capacity for precise determination, indeed, makes its presence or non-presence the only accurate gauge of other immoral acts. Murder, for example, is nowhere regarded as immoral save it involve some repudiation of a social compact, of a tacit promise to refrain from it—in brief, some deceit, some perfidy, some lie. One may kill freely when the pact is formally broken, as in war. One may kill equally freely when it is broken by the victim, as in an assault by a highwayman. But one may not kill so long as it is not broken, and one may not break it to clear the way. Some form of lie is at the bottom of all other recognized crimes, from seduction to embezzlement. Curiously enough, this master immorality of them all is not prohibited by the Ten Commandments, nor is it penalized, in its pure form, by the code of any civilized nation. Only savages have laws against lying per se.