And he changed his behavior - Some imagine David was so terrified at the danger to which he was now exposed, that he was thrown into a kind of frenzy, accompanied with epileptic fits. This opinion is countenanced by the Septuagint, who render the passage thus: Ιδου ιδετε ανδρα επιλητον; "Behold, ye see an epileptic man. Why have ye introduced him to me?" Μη ελαττουμαι επιληπτων εγω; "Have I any need of epileptics, that ye have brought him to have his fits before me, (επιληπτευεσθαι προς με?") It is worthy of remark, that the spittle falling upon the beard, i.e., slavering or frothing at the mouth, is a genuine concomitant of an epileptic fit.

If this translation be allowed, it will set the conduct of David in a clearer point of view than the present translation does. But others think the whole was a feigned conduct, and that he acted the part of a lunatic or madman in order to get out of the hands of Achish and his courtiers. Many vindicate this conduct of David; but if mocking be catching, according to the proverb, he who feigns himself to be mad may, through the just judgment of God, become so. I dare not be the apologist of insincerity or lying. Those who wish to look farther into this subject may consult Dr. Chandler, Mr. Saurin, and Ortlob, in the first volume of Dissertations, at the end of the Dutch edition of the Critici Sacri.

is mad. or, playeth the madman

Ecclesiastes 7:7 Surely oppression makes a wise man mad; and a gift destroys the heart.

Touching Jacob, However, that which He did at his Mother's Bidding...
24. Touching Jacob, however, that which he did at his mother's bidding, so as to seem to deceive his father, if with diligence and in faith it be attended to, is no lie, but a mystery. The which if we shall call lies, all parables also, and figures designed for the signifying of any things soever, which are not to be taken according to their proper meaning, but in them is one thing to be understood from another, shall be said to be lies: which be far from us altogether. For he who thinks this, may …
St. Augustine—Against Lying