“Now all the wells which his father’s servants had dug in the days of Abraham his father, the Philistines stopped up by filling them with earth.” Gen. 26:15
We tend to read this verse as if the Philistines intentionally filled Abraham’s old wells to spite Abraham and possibly Isaac. We recall Abimelech’s oath with Abraham:
“Now it came about at that time that Abimelech and Phicol, the commander of his army, spoke to Abraham, saying, “God is with you in all that you do; now therefore, swear to me here by God that you will not deal falsely with me or with my offspring or with my posterity, but according to the kindness that I have shown to you, you shall show to me and to the land in which you have sojourned.”” Gen. 21:22-23
A few verses later (26:18) we also see Isaac re-digging the wells Abraham had dug. All of this seems to point to and justify that the Philistines are just being vindictive, however I do not believe this is the case.
First consider that although Abraham used to live here in Gerar, Isaac did not live here this entire time but rather came recently to escape a famine (26:1). Second we consider that Abraham is dead. Together this tells us that no one was using Abraham’s wells for some period of time. Third, just as it takes effort to dig a well, it takes effort to fill a well.
If the wells were just sitting there not being used, our initial conclusion may be that they had no good reason to fill them up, other than to spite Abraham in his death and erase any vestiges of his time in Gerar. And so we fall into the same trap of misjudging the motives of our perceived enemies as both Abraham and Isaac did regarding their wives.
However Rashi points out the most plausible explanation: the Philistines likely stopped up the wells to prevent any invading army from having a water source.
As for Isaac re-digging the wells, it is entirely possible that Isaac feels the Philistines are dishonoring his father’s name, however one of the lessons Isaac learns through this ordeal is that just because something was Abraham’s, it is still in Gerar and still the property of the Philistines because Abraham too was just a sojourner there. And though both Abraham and Isaac had quarrels over wells in Gerar, when Abimelech comes to make a peace covenant with each of them, Abraham chooses to complain about the wells (Gen. 21:25), but Isaac does not (Gen. 26:26-33).