For the 1920 LDS edition, the editors changed the second retain in this verse to keep, but the first one was left unchanged. The meaning of retain in both cases is ‘keep back’ (or equivalently, ‘hold back’). Since the preposition from came right after the second retain, the 1920 editors were able to make the replacement for the second retain since the keep in “keep from this people” implies ‘keep back’. The critical text will, of course, maintain both instances of original retain here in Alma 37:27.
One of the problems with the word retain in the Book of Mormon is that it sometimes takes on unexpected meanings. For instance, in Alma 44:8–12 there are at least two, perhaps three, occurrences of this verb with the meaning ‘take back’, even though modern English readers tend to interpret retain in that passage as meaning simply ‘keep’ (for discussion, see under Alma 44:11). Most uses of retain with unexpected meanings have been edited, but others have not (for instance, two of the three instances in Alma 44:8–12). Besides the change of one of the retain’s here in Alma 37:27 to keep, there are two idiosyncratic changes later in the book of Alma, namely, in Alma 39:13 (where retain is deleted) and in Alma 44:11 (where retain is replaced with recall ). There are also seven places where retain is replaced with regain, from Alma 58 through Helaman 4 (see the discussion under Alma 58:3).
Summary: Restore in Alma 37:27 the original retain that was emended in the 1920 LDS edition to keep; the original text for this verse has two instances of the verb retain, each with the meaning ‘keep or hold back’.