John Gill Commentary 1 Samuel 28

And it came to pass in those days
That David was in the country of the Philistines:

that the Philistines gathered their armies together :
out of their five principalities or lordships:

for warfare to fight with Israel ;
with whom they were continually at war, and though sometimes there was a cessation of arms, yet never any settled peace; and the Philistines took every opportunity and advantage against them, as they now did; when David was among them, and so had nothing to fear from him, but rather expected his assistance; and Samuel was dead, and Saul in a frenzy:

and Achish said unto David :
who seems to have been at the head of the combined armies of the Philistines:

know thou assuredly that thou shall go with me to battle, thou and thy
men ;
against Israel; which was a trying thing to David, and whereby he was like to be drawn into a dilemma; either to fight against his country, which he could not do conscientiously; or be guilty of ingratitude to Achish, and incur his displeasure, and be liable to be turned out of his country, or treated in a worse manner, even he and his men, to be seized on and cut to pieces by the forces of the Philistines, should he refuse.

And David said to Achish, surely you shall know what your
servant can do
By which he would have Achish understand, and so he did, that he would exert himself in favour of the Philistines, and against Israel, and do great and brave things, of which Achish would be made sensible, through your heroic courage and valour; though he meant rather what he could and should do for Israel against the Philistines, if he had an opportunity: but it seems best of all to consider David as quite undetermined, and at a loss what to do, hoping that God in his providence would extricate him out of this difficulty, and direct him what he should do, which then Achish would know; and accordingly he was delivered out of it:

and Achish said to David :
putting confidence in him on account of his answer, and believing he was hearty in engaging in the war with the Philistines against Israel:

therefore will I make you keeper of my head for ever ;
the captain of his bodyguard, which post he should hold for life; or he proposed to put him into this post, that he might be with him, near his person, and under his eye, that he might observe how he behaved himself; which may show some suspicion of him.

Now Samuel was dead
Had been so for some time; which is mentioned before, (1 Samuel 25:1); and here repeated, partly to observe the reason of the Philistines renewing the war, and partly to account for the conduct of Saul, in seeking to a witch to raise Samuel, and for the sake of that story:

and all Israel lamented him ;
as they had great reason to do; (See Gill on 1 Samuel 25:1); and buried him in Ramah, even his own city; there being two Ramahs, as Kimchi observes, it is added, "in his own city", to show that he was buried in that Ramah which was his native place, and where his constant residence was; though, as he says, it may mean that he was buried within the city, and not without it; but the Targum gives a different sense, ``and they buried him in Ramah, and mourned for him every man in his city:''

and Saul had put away those that had familiar spirits, and the wizards ,
out of the land :
out of the land of Israel; had by an edict banished them, or had given orders that neither witches nor wizards should abide in the land; but should be taken up, and prosecuted according to the law of God; which he had done either at the instigation of Samuel; or, as some think, from a conceit that the evil spirit he had been troubled with was owing to them; or to make some appearance of a zeal for religion, and the honour and glory of God: this is observed to show the inconstancy of Saul, and his folly in applying after this to a person of such a character, and to account for the fears of the woman when applied to, and afterwards when she was engaged, when she found it was by Saul; see (1 Samuel 28:7–12) .

And the Philistines gathered themselves together
From different parts, and formed a considerable army:

and came and pitched in Shunem ;
a city, in the borders of the tribe of Issachar, of which (See Gill on Joshua 19:18);

and Saul gathered all Israel together, and they pitched in Gilboa ;
a range of mountains, near Jezreel, and which Jerom ^F2 calls the mountains of the Philistines, sixmiles from Scythopolis, where there is a large village called Gelbus.

FOOTNOTES:

• F2: De loc. Heb fol. 92. D.

And when Saul saw the host of the Philistines
From the mountains of Gilboa, where he had pitched his camp:

he was afraid, and his heart greatly trembled ;
on sight of the numbers of them, and thinking perhaps of the death of Samuel, and of the loss of David; who was now among the Philistines, and might possibly fight against him, and for the Philistines, of which he might be informed; however, he was not with him, and his conscience might accuse him of various sins he had been guilty of, for which he might fear the Lord would now reckon with him.