How do we reconcile this Pasuk, which prescribes Sekilah for Ov ve'Yid'oni, with Pasuk 6, which prescribes Kares?
Rashi: The perpetrator is Chayav Kares if there are no witnesses, and Sekilah, if there are.
What is the connection between this Pasuk and the previous Pesukim?
Seforno: Seeing as the objective of all the current Mitzvos is to sanctify Yisrael, anyone who deviates from that, who turns to Ov and Yid'oni whose essence abominates the Soul, deserves to be put to death by stoning.
Ba'al ha'Turim (citing Sifri, Parshas Shoftim): Hashem separated us from the nations to place His Shechinah among us, 1 and we have no need of various types of sorcery to foretell the future like the other nations who have no Navi or anyone of consequence, and who therefore need Ov and Yid'oni.
See Berachos 7a