Or HaChaim on Numbers 25:1/אור החיים על במדבר כ״ה:א׳

1 וישב ישראל בשטים. Israel abode in Shittim, etc. What need was there for the Torah to write this introduction? Tanchuma on our verse explains that the location was a cause for the seduction to succeed. As long as the Israelites had dwelled in the desert instead of in or near populated areas there had not been a single incidence of unchaste behaviour. The Torah may have indicated that this place was singularly apt to arouse the animalistic instincts in man. The immediate cause may have been that the Israelites took strolls in the neighbourhood of their camp and encountered Moabite women. The Torah's emphasis on וישבו may be because instead of merely going for a stroll they made themselves at home there. The root of the word שטים occurs in Numbers 11,8 where the Torah describes the daily stroll to pick up the manna with the words שטו העם ולקטו.

2ויתל העם לזנות אל בנות מואב, The people debased themselves to commit harlotry with the daughters of Moav. The word ויחל may be understood as profaning oneself. The word זנות implies the straying after alien deities. The reason the Torah coined the unusual construction אל בנות, instead of עם בנות, or something similar, has been explained by Tanchuma to indicate that the daughters of Moav did not offer themselves to the Israelites without conditions, but demanded that these first commit an act of obeisance to one of their deities. The Torah hints by the word אל that the Israelites who became guilty of this extracurricular sex had first bowed TO something that the daughters of Moav customarily bowed to. The Torah makes a point of describing the Israelites who became guilty of this aberration as only העם. The spiritual elite, who are customarily referred to as Israelites, was not involved.