C. F. Keil and Franz Delitzsch on 1 Samuel 20:1

After the occurrence which had taken place at Naioth, David fled thence and met with Jonathan, to whom he poured out his heart.According to Ewald and Thenius, this chapter was not written by the author of the previous one, but was borrowed from an earlier source, and 1Sa 20:1 was inserted by the compiler to connect the two together. But the principal reason for this conjecture - namely, that David could never have thought of sitting at the royal table again after what had taken place, and that Saul would still less have expected him to come - is overthrown by the simple suggestion, that all that Saul had hitherto attempted against David, according to 1Sa 19:8., had been done in fits of insanity (cf. 1Sa 19:9.), which had passed away again; so that it formed no criterion by which to judge of Saul’s actual feelings towards David when he was in a state of mental sanity.

Though he had been delivered for the moment from the death which threatened him, through the marvellous influence of the divine inspiration of the prophets upon Saul and his messengers, he could not find in this any lasting protection from the plots of his mortal enemy. He therefore sought for his friend Jonathan, and complained to him, “What have I done? what is my crime, my sin before thy father, that he seeks my life?”