Or HaChaim on Numbers 22:36/אור החיים על במדבר כ״ב:ל״ו

1 ויצא לקראתו אל עיר מואב, He came to welcome him to the city of Moav. Why did the Torah have to bother to tell us where the meeting between Bileam and Balak took place? Perhaps the Torah wanted to show us that Balak did not hold Bileam in high esteem. Although Balak had heard that Bileam was on his way, he did not leave his city to prepare a welcome such as one does for highly placed visitors. He was content to await Bileam's arrival before welcoming him.

2ויצא לקראתו אל עיר מואב אשר על גבול ארנון אשר בקצה הגבול. Why all these details about the location of the border? Perhaps the Torah wanted to tell us that if Balak did trouble himself to go to the border of Moav which was close to his capital, he did not do so in order to honour Bileam but that he had a different reason. Bamidbar Rabbah 20,16 explains that the reason Balak went to this border was to tell Bileam that this border had been established already in times of Noach [not literally speaking as Moav was not founded till after Abraham's time. Ed.] He wanted to show Bileam how both Og and Sichon had been guilty of violating these longstanding borders. At any rate, if not for these political considerations, Balak would not have troubled himself to come out towards Bileam even this little distance.