A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
1 Kings (1 Samuel) 18:1
sa1 18:1JONATHAN LOVES DAVID. (Sa1 18:1-4)
the soul of Jonathan was knit with the soul of David--They were nearly of an age. The prince had taken little interest in David as a minstrel; but his heroism and modest, manly bearing, his piety and high endowments, kindled the flame not of admiration only, but of affection, in the congenial mind of Jonathan.
1 Kings (1 Samuel) 18:2
sa1 18:2Saul would let him go no more home--He was established as a permanent resident at court.
1 Kings (1 Samuel) 18:3
sa1 18:3Then Jonathan and David made a covenant--Such covenants of brotherhood are frequent in the East. They are ratified by certain ceremonies, and in presence of witnesses, that the persons covenanting will be sworn brothers for life.
1 Kings (1 Samuel) 18:4
sa1 18:4Jonathan stripped himself of the robe that was upon him, and gave it to David--To receive any part of the dress which had been worn by a sovereign, or his eldest son and heir, is deemed, in the East, the highest honor which can be conferred on a subject (see on Est 6:8). The girdle, being connected with the sword and the bow, may be considered as being part of the military dress, and great value is attached to it in the East.
1 Kings (1 Samuel) 18:6
sa1 18:6SAUL ENVIES HIS PRAISE. (Sa1 18:5-9)
the women came out of all cities of Israel--in the homeward march from the pursuit of the Philistines. This is a characteristic trait of Oriental manners. On the return of friends long absent, and particularly on the return of a victorious army, bands of women and children issue from the towns and villages, to form a triumphal procession, to celebrate the victory, and, as they go along, to gratify the soldiers with dancing, instrumental music, and extempore songs, in honor of the generals who have earned the highest distinction by feats of gallantry. The Hebrew women, therefore, were merely paying the customary gratulations to David as the deliverer of their country, but they committed a great indiscretion by praising a subject at the expense of their sovereign.
1 Kings (1 Samuel) 18:9
sa1 18:9Saul eyed David--that is, invidiously, with secret and malignant hatred.
1 Kings (1 Samuel) 18:10
sa1 18:10SEEKS TO KILL HIM. (Sa1 18:10-12)
on the morrow, that the evil spirit from God came upon Saul--This rankling thought brought on a sudden paroxysm of his mental malady.
he prophesied--The term denotes one under the influence either of a good or a bad spirit. In the present it is used to express that Saul was in a frenzy. David, perceiving the symptoms, hastened, by the soothing strains of his harp, to allay the stormy agitation of the royal mind. But before its mollifying influence could be felt, Saul hurled a javelin at the head of the young musician.
there was a javelin in Saul's hand--Had it been followed by a fatal result, the deed would have been considered the act of an irresponsible maniac. It was repeated more than once ineffectually, and Saul became impressed with a dread of David as under the special protection of Providence.
1 Kings (1 Samuel) 18:13
sa1 18:13FEARS HIM FOR HIS GOOD SUCCESS. (Sa1 18:13-16)
Therefore Saul removed him from him--sent him away from the court, where the principal persons, including his own son, were spellbound with admiration of the young and pious warrior.
made him captain over a thousand--gave him a military commission, which was intended to be an honorable exile. But this post of duty served only to draw out before the public the extraordinary and varied qualities of his character, and to give him a stronger hold of the people's affections.
1 Kings (1 Samuel) 18:17
sa1 18:17HE OFFERS HIM HIS DAUGHTER FOR A SNARE. (Sa1 18:17-21)
Saul said to David, Behold my elder daughter Merab, her will I give thee to wife--Though bound to this already [Sa1 17:25], he had found it convenient to forget his former promise. He now holds it out as a new offer, which would tempt David to give additional proofs of his valor. But the fickle and perfidious monarch broke his pledge at the time when the marriage was on the eve of being celebrated, and bestowed Merab on another man (see on Sa2 21:8); an indignity as well as a wrong, which was calculated deeply to wound the feelings and provoke the resentment of David. Perhaps it was intended to do so, that advantage might be taken of his indiscretion. But David was preserved from this snare.
1 Kings (1 Samuel) 18:20
sa1 18:20Michal Saul's daughter loved David--This must have happened some time after.
they told Saul, and the thing pleased him--Not from any favor to David, but he saw that it would be turned to the advancement of his malicious purposes, and the more so when, by the artful intrigues and flattery of his spies, the loyal sentiments of David were discovered.
1 Kings (1 Samuel) 18:25
sa1 18:25The king desireth not any dowry--In Eastern countries the husband purchases his wife either by gifts or services. As neither David nor his family were in circumstances to give a suitable dowry for a princess, the king intimated that he would be graciously pleased to accept some gallant deed in the public service.
a hundred foreskins of the Philistines--Such mutilations on the bodies of their slain enemies were commonly practised in ancient war, and the number told indicated the glory of the victory. Saul's willingness to accept a public service had an air of liberality, while his choice of so difficult and hazardous a service seemed only putting a proper value on gaining the hand of a king's daughter. But he covered unprincipled malice against David under this proposal, which exhibited a zeal for God and the covenant of circumcision.
1 Kings (1 Samuel) 18:26
sa1 18:26the days were not expired--The period within which this exploit was to be achieved was not exhausted.
1 Kings (1 Samuel) 18:27
sa1 18:27David . . . slew of the Philistines two hundred men--The number was doubled, partly to show his respect and attachment to the princess, and partly to oblige Saul to the fulfilment of his pledge.
1 Kings (1 Samuel) 18:29
sa1 18:29Saul was yet the more afraid of David--because Providence had visibly favored him, by not only defeating the conspiracy against his life, but through his royal alliance paving his way to the throne.