Adam Clarke on John 4:20

Worshipped in this mountain - Probably pointing to Mount Gerizim, at the foot of which Sychar was situated. The patriarchs had worshipped here-Jacob builded an altar on this mountain, and worshiped the true God: see Gen 22:2; Gen 33:20. Thus she could say, Our fathers worshipped in this mountain. On this mountain Sanballat had built them a temple, about 332 years before our Lord's incarnation. See Joseph. Antiq. xi. c. viii. s. 4, and 2 Maccabees 6:2.

Many heathens considered particular places as having a peculiar sanctity or fitness, for the worship of their deities, beyond others. Such places abound in Hindostan; and in them they think men ought to worship.

In the Hebrew Pentateuch, Deu 27:4, etc., where the Israelites are commanded to build an altar on mount Ebal, and offer sacrifices, etc., the Samaritan Pentateuch has Gerizim instead of Ebal; and Dr. Kennicott strongly contends, Dissert. vol. ii. p. 20, etc., that Gerizim is the genuine reading: but our blessed Lord, by the following answer, shows that the place was a matter of little importance, as the Divine worship was no longer to be confined to either: Joh 4:21. See the note on Deu 27:4.