Exegesis:
hōs gegraptai ‘as it is written,’ the usual formula for the introduction of a quotation from the Old Testament. The subsequent quotation, here related to what precedes by the connective hōs ‘as,’ serves to qualify John’s ministry in a general way as the announcing of the promised salvation and has no direct bearing upon the baptism he proclaims.
en biblō logōn Ēsaiou tou prophētou ‘in the book of sayings of Isaiah the prophet.’
biblos (also 20.24) ‘book,’ in both places followed by a genitive which indicates the content of the book. As the synonymous biblion it is to be thought of as a scroll (cf. Plummer on 4.20).
phōnē boōntos ‘(the) voice of one shouting,’ the genitive boōntos makes phōnē, which is without article, definite. The phrase serves to draw the attention strongly to what follows, cf. Phillips‘ “Hark! Someone is shouting”.
boaō ‘to shout,’ ‘to cry out,’ here of solemn proclamation.
en tē erēmō ‘in the desert,’ goes with boōntos, not with what follows, as in the Hebrew text of Is. 40.3.
hetoimasate tēn hodon kuriou ‘prepare the road of the Lord.’ The underlying picture is that of preparations for an approaching visit of a king (cf. Moulton-Milligan 258): the road over which the Lord shall come must be made ready. The plural shows that the order is directed to a group but this group is not subsequently identified. The picture is that of an existing road which must be made ready.
eutheias poieite tas tribous autou ‘make his paths straight.’ The reference is to the elimination of curves, rather than to making the road smooth, as shown by the use of euthus ‘straight’ elsewhere and by the fact that in v. 5 the same word eutheias is used in contrast with skolios ‘bent,’ ‘curved,’ and distinguished from leios ‘smooth.’
eutheia (†, from masc, euthus) ‘straight.’ In v. 5 it is used as a substantive with hodon ‘way’ understood, and meaning ‘straight way.’
tribos ‘a beaten track,’ ‘path.’
Translation:
This verse, in the Greek subordinated to v. 3, may better become a new sentence, e.g. ‘This happened just as it was written in…’ (Marathi), ‘This is according to what…’ (cf. Manobo). A more radical shift of order is required in Telugu, which first quotes the prophecy, and concludes this quotation with the statement that these occurrences were predicted by Isaiah.
As it is written in … For this formula to introduce quotations from the Old Testament see above on 2.23. The pronoun it refers to the details of John’s ministry as described in v. 3, cf. “all in accordance with” (The Four Gospels – a New Translation); if necessary, one may shift to a personal reference, e.g. ‘About him it has been written in…,’ or, ‘He was like the man mentioned in….’
The book of the words of Isaiah the prophet, i.e. the book containing the words of the prophet Isaiah, or, the book recording what the prophet Isaiah has said. Idiom may necessitate some adjustments, e.g. ‘the words recorded in the book (of prophecies) of the prophet Is.’ (Chinese Union Version) or the ‘words of the prophet Is., (as) recorded/contained in his book.’ If idiom, style, or decodability require a simpler wording, the rendering may be modelled on the synonymous phrase “the book of the prophet Is.” (4.17) as done in Marathi, Balinese, or it may become, ‘in the (book of the) prophecies of (Prophet) Is.’ (cf. Malay and Bahasa Indonesia RC). Still further simplification will be necessary where passive constructions and subordination have to be avoided; then the whole clause “it is written … Isaiah” may be rendered, “as the prophet Is. had written in his book” (Good News Translation). For book see also on 4.17.
The voice of one crying in the wilderness. One (or, a person) crying has been rendered by the more specific ‘a proclaimer’ (Marathi, which also changes the phrase in a full sentence by adding a verb, ‘happened’). In Manobo culture ‘crying/shouting’ implies anger and accordingly has to be avoided. In such a case one may shift to ‘the voice of a person was widely heard.’
For prepare the way of the Lord, make his paths straight. — Prepare the way of. One of the renderings possible in Sranan Tongo is ‘clear the overgrown tracks for (lit. wake up the lines for).’ Way and paths, or ‘road(s)’ and ‘little roads,’ ‘path(s)’ and ‘by-paths/side-alleys’; or, not to overtranslate the difference, ‘passage (or, place to walk)’ and ‘ways/paths,’ or a noun and a pronominal reference, e.g. ‘prepare the way…, and make it straight.’
Lord, see above on 1.6, sub (c).
Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.