The "way of the land of the Philistines" describes a small portion of the route later known as the Via Maris, "the Way of the Sea." This coastal road connected the Nile Delta region with Canaan, Syria, and beyond that to Mesopotamia. Although the naming of this portion of the road after the Philistines may be a slight anachronism (perhaps a later emendation), Philistines already lived along its southern course in Canaan.
However, more significant is the Philistines' connection with war. Evidently, the people who lived along that road were a hostile group, easily provoked into armed conflict, and at the time of the Exodus, on a war footing. The fledgling nation of Israel, God knew, was not yet prepared to fight any people as aggressive as the Philistines, no matter what their numbers were at the time.
Nevertheless, this passing mention in Exodus 13 alludes to the fact that the Philistine presence in southern Canaan had not remained static. From a trading outpost in Gerar, they had expanded in the intervening four centuries to control a large area. Perhaps they were not the most populous of the ethnic groups there, but they were certainly the dominant one. It is thought that their numbers were steadily increased by new colonists from their homeland in the Aegean. In addition, it seems to have been a conscious policy to assimilate to a large degree with the native population, which would include intermarriage and adoption of local deities. In this way a minority people could quickly rise to prominence.
Richard T. Ritenbaugh
Who Were the Philistines?