1 Samuel 20:13 - Matthew Poole's English Annotations on the Holy Bible

The Lord give thee that honour and success in all thy affairs which he hath given to my father. Jonathan undoubtedly knew of Samuel's final and irrevocable sentence of Saul's rejection from the kingdom, and of the substitution of some other person after God's own heart in his stead; and that David was this person he might strongly suspect, (that which even Saul suspected,) both from his eminent piety, and wisdom, and valour, and universal worth, and from the great things which God had done, both by him and for him, in preserving and advancing him by such unusual methods; and it is most likely that Jonathan did ask David about it, and that David did faithfully inform him of the whole truth, as may be gathered both from the words here following, and from 1 Samuel 23:17. And that the knowledge hereof did not raise jealousy, and envy, and rage in him, who was the next heir of the crown, as it did in his father, must be ascribed to Jonathan's piety towards God, to whose disposal he cheerfully submitted himself, and to his sincere friendship to David, in whose happiness he rejoiced as in his own.