It's from the Rokeach's book Sodei Razei Smuchim ([link][1]).

Edit: He seems to be clarifying a statement in [the gemara][2] regarding learning ideas via juxtaposition of certain words and verses (smichut) in the Torah. One view in the gemara is that there are ideas to be learnt via juxtaposition. Another view is that there aren't, except with regards to Devarim, AKA Sefer Mishneh Torah. The Rokeach is apparently explaining why even accordung to those who disagree with the notion of smichut, it can still be learned in Devarim - because of the stated gematria connection. The Rokeach's book, however, seems to follow the first opinion, and presents Smichut concepts from the entirety of the Torah.

For general information regarding the book, see [here][3] (PDF link)


  [1]: https://tablet.otzar.org/#/book/143645/p/13/t/827980/fs/muMMBSv3YbyncfpOmhP8TBnj245zR2jZtMk6kIPaXYmP/start/0/end/41/c
  [2]: https://www.sefaria.org.il/Yevamot.4a.4?vhe=William_Davidson_Edition_-_Vocalized_Aramaic&lang=bi&p2=Berakhot.21b.9&lang2=bi
  [3]: https://forum.otzar.org/download/file.php?id=68538