Charles Ellicott Commentary 1 Samuel 20:2

"And he said unto him, Far from it; thou shalt not die: behold, my father doeth nothing either great or small, but that he discloseth it unto me; and why should my father hide this thing from me? it is not so." — 1 Samuel 20:2 (ASV)

God forbid; thou shalt not die. —Jonathan even now refuses to believe that his loved father, when he was himself, really wished ill to David; all that had until then happened the princely Jonathan put down to his father’s unhappy malady. He urges upon his friend that if the king seriously had designs upon David’s life, he would in his calm, lucid days have consulted with him, Jonathan, to whom he always confided all his State secrets.

Will do nothing. —Here the commentators and the versions—LXX, Vulgate, and Chaldee—all agree to read in the Hebrew text, lo “not,” for lo “to him,” that is, for a vau an aleph must be substituted.