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
gen 26:1SOJOURN IN GERAR. (Gen. 26:1-35)
And there was a famine in the land . . . And Isaac went unto . . . Gerar--The pressure of famine in Canaan forced Isaac with his family and flocks to migrate into the land of the Philistines, where he was exposed to personal danger, as his father had been on account of his wife's beauty; but through the seasonable interposition of Providence, he was preserved (Psa 105:14-15).
gen 26:12Then Isaac sowed in that land--During his sojourn in that district he farmed a piece of land, which, by the blessing of God on his skill and industry, was very productive (Isa 65:13; Psa 37:19); and by his plentiful returns he increased so rapidly in wealth and influence that the Philistines, afraid or envious of his prosperity, obliged him to leave the place (Pro 27:4; Ecc 4:4). This may receive illustration from the fact that many Syrian shepherds at this day settle for a year or two in a place, rent some ground, in the produce of which they trade with the neighboring market, till the owners, through jealousy of their growing substance, refuse to renew their lease and compel them to remove elsewhere.
gen 26:15all the wells which his father's servants had digged . . . the Philistines had stopped, &c.--The same base stratagem for annoying those against whom they have taken an umbrage is practiced still by choking the wells with sand or stones, or defiling them with putrid carcases.
gen 26:17valley of Gerar--torrent-bed or wady, a vast undulating plain, unoccupied and affording good pasture.
gen 26:18Isaac digged again the wells of water--The naming of wells by Abraham, and the hereditary right of his family to the property, the change of the names by the Philistines to obliterate the traces of their origin, the restoration of the names by Isaac, and the contests between the respective shepherds to the exclusive possession of the water, are circumstances that occur among the natives in those regions as frequently in the present day as in the time of Isaac.
gen 26:26Then Abimelech went to him--As there was a lapse of ninety years between the visit of Abraham and of Isaac, the Abimelech and Phichol spoken of must have been different persons' official titles. Here is another proof of the promise (Gen 12:2) being fulfilled, in an overture of peace being made to him by the king of Gerar. By whatever motive the proposal was dictated--whether fear of his growing power, or regret for the bad usage they had given him, the king and two of his courtiers paid a visit to the tent of Isaac (Pro 16:7). His timid and passive temper had submitted to the annoyances of his rude neighbors; but now that they wish to renew the covenant, he evinces deep feeling at their conduct, and astonishment at their assurance, or artifice, in coming near him. Being, however, of a pacific disposition, Isaac forgave their offense, accepted their proposals, and treated them to the banquet by which the ratification of a covenant was usually crowned.
gen 26:34Esau . . . took to wife--If the pious feelings of Abraham recoiled from the idea of Isaac forming a matrimonial connection with a Canaanitish woman [Gen 24:3], that devout patriarch himself would be equally opposed to such a union on the part of his children; and we may easily imagine how much his pious heart was wounded, and the family peace destroyed, when his favorite but wayward son brought no less than two idolatrous wives among them--an additional proof that Esau neither desired the blessing nor dreaded the curse of God. These wives never gained the affections of his parents, and this estrangement was overruled by God for keeping the chosen family aloof from the dangers of heathen influence.