Quoted from Isaiah 29:13.
“Moreover.” This comes from the quote in the Septuagint, the Greek translation of the Old Testament. See Lenski, Matthew, p. 587.
“doctrines.” The Greek word is didaskalia (#1319 διδασκαλία), a noun, and it has two primary meanings: It is used of the act of teaching or instruction (as if it was a verb), and it is also used for what is taught, i.e., the doctrine or material that was presented. In this verse we felt “doctrine” was better than “teaching.” [For more on didaskalia see commentary on 1 Tim. 4:13].