The instant she perceived this, she proposes what she thought the most important of all questions. This mountain — Pointing to Mount Gerizim. Sanballat, by the permission of Alexander the Great, had built a temple upon Mount Gerizim, for Manasseh, who for marrying Sanballat's daughter had been expelled from the priesthood and from Jerusalem, Nehemiah 13:28. This was the place where the Samaritans used to worship in opposition to Jerusalem. And it was so near Sychar, that a man's voice might be heard from the one to the other. Our fathers worshipped — This plainly refers to Abraham and Jacob (from whom the Samaritans pretended to deduce their genealogy) who erected altars in this place: Genesis 12:6-7, and Genesis 33:18, Genesis 33:20. And possibly to the whole congregation, who were directed when they came into the land of Canaan to put the blessing upon Mount Gerizim, Deuteronomy 11:29. Ye Jews say, In Jerusalem is the place — Namely, the temple.
Related Commentaries of John 4:20
John 4:20
20 Our fathers worshipped in this mountain; and ye say, that in Jerusalem is the place where men ought to worship.