One wonders here in 2 Nephi 26:20 if the singular face (the reading of 𝓟, the earliest textual source) might be an error for the plural faces. Note first that the phraseology “grind (upon) the face(s) of the poor” does occur elsewhere in the text:
Here both the King James passage and the Book of Mormon text have the plural faces.
Errors elsewhere in the text indicate that sometimes the singular face may be an error for the plural faces. Consider the following example, which is also an Isaiah quote:
The corresponding Isaiah passage in the King James Bible has the plural reading faces, which supports the plural of the earliest textual sources in Mosiah 14:3. In this case, the 1837 edition accidentally replaced the plural faces with face.
Another example of variation for face(s) is found later in the Book of Mormon text:
The original manuscript is not extant for this case of face (“the face of angels”), but the earliest reading (in 𝓟) does clearly seem to be an error, especially given the two corresponding occurrences of “the faces of Nephi and Lehi” in this passage. The 1837 edition emended the text here to read in the plural (“the faces of angels”), which may be the original reading. If so, then this passage would provide another example of faces being accidentally changed to face. For further discussion, see Helaman 5:36–37.
There are four additional biblical quotations in the Book of Mormon that refer to the face(s) of more than one person. Two of these have the plural faces, just like their corresponding King James passages:
The two other cases cite a single Isaiah passage:
In the Book of Mormon text, one of these citations has the singular face, but the other one has the plural faces:
Clearly, the singular face is intended in 1 Nephi 21:23 since the corresponding King James text also has the singular. In general, however, the Book of Mormon text prefers the plural faces when referring to more than one person, as in the case of 2 Nephi 6:7. For further discussion of this variability regarding face(s) (including its Hebrew basis in the Isaiah quotations), see 2 Nephi 6:7.
Despite all of this argumentation, it should be noted that the use of the singular face in 1 Nephi 21:23 and 2 Nephi 26:20 is not at all objectional. The singular face in 1 Nephi 21:23 works since the text can be interpreted as if it read “they shall each bow down to thee with their face towards the earth”. As for 2 Nephi 26:20, the singular face is acceptable because the corresponding poor is also singular in form, even though the intended number is plural. Further, this lack of difficulty in both cases would explain why there has been no tendency in the history of the text to emend face in 2 Nephi 26:20 (or in 1 Nephi 21:23) to read in the plural. Consequently, the critical text will accept the singular face here in 2 Nephi 26:20 (the reading of the printer’s manuscript, the earliest textual source). The possibility remains, of course, that the singular face in 2 Nephi 26:20 may be an error (for faces) that entered the text early on in its transmission.
Summary: Maintain in 2 Nephi 26:20 the singular face since it will work (“and grind upon the face of the poor”), even though it is possible that the original text read faces, as it does in 2 Nephi 13:15 (“and grind the faces of the poor”).