in which he teaches that all nusachim (textual versions) of prayer are valid, as long as God is worshipped with proper intent
In the days of Minister Shalom (Rabbi Shalom Rokeach, 1781 – 1855) some sages of that generation felt that the entire public should pray according to the custom maintained in the Land of Israel and use the Sepharad version of the siddur prayer book. They advised that those who were still accustomed to the Tachlal (Yemenite custom) version should be given Sepharad siddurim by the Nassi (president) of the community, so that they would all become accustomed to a unified version of prayers; the Nassi agreed to this. The rabbis accustomed to praying according to the Tachlal version then arose… and wrote announcements in the form of decrees stating that changing forefathers' customs is forbidden, based on ancient texts and on subsequent writings by Maimonides. When the wise people of both parties realized that the fire of debate had been ignited for no good reason – since one was as valid and desirable as the other, as long as God is worshipped with proper and pure intent - they convened and agreed to quell the quarrel with amendments that calmed the spirits of both factions, amendments that reconciled the opinions in peace, love and brotherhood.
Sa'arat Teiman, p. 18, published by the author, Rav Kook Institute and The Ministry of Education, Jerusalem (1954).