As existing answers note: (1) "messiah" (Hebrew mashiach) and "christ" (Greek christos) are equivalent words meaning "anointed one", and in the context of Graeco-Roman Judaism and early Christianity these were technical terms referring to a future agent of divine deliverance. And (2), in the gospel of John, Hebrew and Aramaic words are regularly translated for readers: see 1:38,41,42; 9:7; 19:17; 20;16. These are all given as parenthetical asides by the evangelist.
OP asks about two such cases, and 1:41, and 4:25. The facts noted above are sufficient for explaining 1:41, and it features in the list of such texts under my (2), above.
The Strange Case of 4:25
However, 4:25 calls for a slightly different explanation, even though it, too, is a parenthetical explanation in context. Typically when "translation explanations" are provided in gJohn, either the verb μεθερμηνεύω methermēneuō or ἑρμηνεύω hermēneuō -- related, obviously, meaning something like "interpret" or "translate" -- is used. In 4:25 the formulation is slightly different:
...he who is called [ὁ λεγόμενος ho legomenos] Christ...
using a participial form of the verb λέγω legō, "to speak". There are two occasions when this verb is used to explain a translation, 19:17 and 20:16; but in both of these it is made explicitly clear that a translation is being offered.
There are, however, a number of places where gJohn offers an alternate designation for identifying an individual using λεγόμενος: John 9:11 (referring to Jesus himself), and John 11:16; 20:24; and 21:2, each of which identifies Thomas as "the Twin" (Θωμᾶς ὁ λεγόμενος Δίδυμος).
Why should this formulation be used in 4:25, then?
It is widely noted in the commentaries that Samaritans did not have a specifically messianic expectation. Rather, the Samaritan hope was to look towards the "Taheb" -- a "returning one" or "restoring one" (rather than "anointed one"), a coming prophet like Moses (not a king like David) who would inaugurate a reign of beatific peace.1
Commentators sometimes pause at 4:25 to reflect that the Samaritan "woman at the well" was not expecting a messiah, but a taheb. However, as noted by John Bowman and repeated by commentators after him, the discussion that unfolds is very much in "Samaritan" terms, even though the nomenclature is "Jewish".2
Now, it's possible that this information isn't needed to see that in John 4:25 "Christ" is to "Messiah" as "Didymus" is to "Thomas" in later passages, that is, an alternate designation for the individual in question. But it does highlight the further linguistic adjustment that gJohn makes in recounting the story in John 4.
So to return to OP's question, then:
Why does John use interpreted/μεθερμηνευόμενον if the Messiah is called/λεγόμενος Christ?
I put this together as follows:
- 1:41 follows John's normal practice of explaining in Greek the Hebrew/Aramaic technical terms, etc., for his readers;
- but in 4:25, having already established the translation equivalence in 1:41 of "christ" and "messiah", he records the same pair this time as alternate designations of the same (expected) individual.
That is, I confess, speculative -- but informed, I hope, by the evidence provided by the book itself, and respecting the patterns it contains.
- For these details and more, see Alan Crown's review of F. Dexinger's 1986 monograph, Der Taheb, in The Jewish Quarterly Review n.s. 80 (1989): 139-141; and cf. Ferdinand Dexinger, "Die Taheb-Vorstellung als Politische Utopie", Numen 37 (1990): 1-23.
- John Bowman, "Samaritan Studies", Bulletin of the John Rylands Library 40 (1958): 298-327 (see pp. 299ff.).