Exegesis:
The syntactic structure of this verse is rather loose. The main clause proeleusetai enōpion autou ‘he will go before him,’ etc. is followed by two infinitive clauses, one (1) with the loosely attached final epistrepsai ‘to turn,’ the other (2) with the unconnected final hetoimasai ‘to prepare.’ Clause (2) is either subordinate to (1), or dependent upon the main clause and then co-ordinate with (1). The former interpretation (represented by The Four Gospels – a New Translation, Willibrord, La Sainte Bible: Nouvelle version Segond révisée) seems to be slightly more probable, since clause (2) is the more general and comprehensive of the two, but the syntactic pattern is too vague to admit of clear distinctions. The semantic function of the clause beginning with hetoimasai however is clear: it serves to indicate with what intention John will ‘turn the hearts of the fathers to the children and the disobedient to the wisdom of the just’: it is to prepare a people for the Lord.
kai autos proeleusetai enōpion autou ‘and he will go before him.’
kai autos ‘and he,’ unemphatic: there appears to be no reason for referring explicitly to the subject because it is the same as that of the preceding verb epistrepsei ‘he will turn’ (different in 1.22; 2.28, which see).
proerchomai ‘to go before,’ as a forerunner (here) or as a leader (22.47).
enōpion autou ‘before him,’ cf. on v. 15. Here it has both a local meaning, ‘some distance in front of him,’ and a temporal one ‘going and coming sometime before him.’ From the general usage of enōpion it follows that the local meaning is predominant.
en pneumati kai dunamei Eliou ‘in the spirit and power of Elijah,’ i.e. “possessed by the spirit and power of Elijah” (New English Bible). en means here as in 2.27 ‘under the influence of,’ or ‘guided by.’ The genitive Eliou is not possessive but qualifying: John will be possessed by the same spirit as Elijah. pneuma does not refer to the human spirit but to the divine spirit, as usually when accompanied by a semantically related noun.
dunamis ‘power,’ often connected with pneuma (4.14; Acts 1.8; Rom 15.13, 19; 2 Tim. 1.7) and here practically synonymous with it as in 1.35. Hence both words may be rendered as one concept, ‘powerful spirit.’
epistrepsai kardias paterōn epi tekna ‘to turn the hearts of the fathers to the children,’ a free quotation of Mal. 4.6 (3.24 in the Hebrew text); the emphasis is on the restoration of mutual relationship between fathers and children. Translations like “to reconcile father and child” (New English Bible, cf. Phillips, An American Translation) are based on the idea of the Hebrew of Mal. 3.23 rather than on the exact wording of Lk. 1.17! The clause may refer to a restoration of parental affection (Plummer, Creed, Klostermann, Weiss) or to the winning of the older generation for the religious ideals of the younger generation (Zahn, Grundmann).
kai apeitheis en phronēsei dikaiōn ‘and the disobedient to the wisdom of the righteous.’ The phrase is still dependent upon epistrepsai, which implies that en phronēsei is equivalent to eis phronēsin, indicating to which John will turn the disobedient. For dikaios cf. on v. 6.
apeithēs ‘disobedient,’ here in the religious sense of ‘disobedient towards God.’
phronēsis ‘way of thinking,’ or, ‘insight,’ ‘understanding.’ The translation “wisdom” (Revised Standard Version and many others) goes back to the latter, “ways” (New English Bible) to the former, which seems to suit the context better.
hetoimasai kuriō laon kateskeuasmenon ‘to make ready for the Lord a people prepared,’ indicating the final purpose of the preceding clause.
hetoimazō ‘to make ready,’ ‘to prepare,’ virtually synonymous with kataskeuazō, but used with a different function: hetoimasai, qualified by kuriō, refers to the act done by John for the Lord, kateskeuasmenon, past participle, refers to the outcome of the act (as brought out by Translator’s New Testament, “thoroughly prepared”). Some translations take kuriō to go with kateskeuasmenon and render hetoimasai and kateskeuasmenon by one expression, cf. “to make a people perfectly ready for the Lord” (An American Translation), but the position of kuriō immediately after hetoimasai and separated from kateskeuasmenon does not point to this interpretation.
kataskeuazō (also 7.27) ‘to make ready,’ ‘to prepare.’
Translation:
Him, or, ‘the Lord,’ because the mere pronoun sounds disrespectful (Malay), cf. on 3.22.
In the spirit and power. As shown in Exegesis the function of “in” often has to be described, e.g. by ‘bearing,’ ‘endowed with’ (Kannada), ‘having received’ (Shipibo-Conibo); with necessary further shifts and expansions this may lead to such renderings of the phrase as, ‘being dressed-in the spirit and having-as-attribute the power’ (Javanese), ‘having-as-spirit the spirit and having-as-power the power,’ ‘having received the powerful/strong spirit,’ or to corresponding verbal clauses. For spirit, preferably to be rendered as in ‘Holy Spirit,’ see references on v. 15; for power on v. 35.
Of Elijah, i.e. that (the prophet) E. had, cf. ‘bespirited and bepowered as E. (was)’ (Batak Toba 1885), ‘his strength of spirit (will be) like the strength of spirit of E.’ (Tae’ 1933), ‘and the spirit and power that have influenced (or, driven/strengthened) E. also will influence (etc.) him.’
To turn the hearts of the fathers to the children repeats the verb of v. 16 but in different context; hence, the rendering may have to differ more or less radically, as in, ‘make the fathers love their children’ (Pohnpeian), ‘direct the hearts of the fathers towards their children’ (Toraja-Sa’dan), ‘cause men to think well again of their children’ (Apache, where ‘father’ cannot be used without definite possessor; hence, ‘men’). The plural in ‘hearts’ is distributive, that in ‘fathers’ and ‘children’ collective, expressing a category; in both cases some languages use a singular. The word (also occurring in 1.51, 66; 2.19, 35, 51; 3.15; 5.22; 6.45; 8.12, 15; 9.47; 10.27; 12.34; 16.15; 18.1; 21.34; 24.25, 32, 38) stands for the centre of the personality, the seat of emotions and/or intellect, etc. Here, as in some other cases, its use helps to signal the metaphorical meaning the verb has. In other languages, however, a direct reference to the person concerned is preferable, see some of the renderings quoted above. In Kituba a literal rendering would imply that a physical transaction was taking place, a quite dangerous idea in the local cultural context, which is avoided by saying, ‘to return fathers to love their children.’ — Fathers. The plural is distributive. For the noun, here used in the sense of a person’s biological father (also in 1.59, 62, 67; 8.51; 9.42, 59; 11.11; 12.53; 14.26; 15.12, 17f, 20ff, 27ff; 16.27; 18.20; and in 2.33, 48. For father(s), i.e. ‘ancestor(s)’ cf. below on 1.32 and 55; for Father in the sense of Jesus’ or the believers’ heavenly Father on 2.49.
And the disobedient to the wisdom (preferably, way of thinking) of the just. To clarify the clause structure the verb rendering “to turn” often has to be repeated here, or a synonymous verb that fits this phrase better, cf. ‘cause the hard-headed to accept the same thoughts as the people who do right’ (Sranan Tongo), ‘cause those who do not hear/obey to hear/obey the wisdom of the men who are good’ (Apache), ‘change the rebellious ones to think as the righteous think’ (Western Highland Purepecha). For disobedient, i.e. ‘those who do not obey God’ (Tboli), cf. the above quotations, and Shipibo-Conibo’s ‘the not to be talked to,’ i.e. people who, though you tell them, do not want to do. For the verb ‘obey’ see on 2.51. For just cf. references on “righteous” in v. 6.
To make ready … prepared, or as a co-ordinated clause, ‘and so (he will) make ready prepared.’ In translating this phrase the main problem is to prevent its sounding repetitive, or becoming a tautology. This will influence the way the verb and the participle must be rendered. Make ready for the Lord, or, ‘form … for the Lord’ (Willibrord, Bible en français courant), ‘makes the hearts soft for the Lord’ (Huanuco Quechua); or again, because the phrase emphasizes the beneficiary, ‘to put at the Lord’s disposal,’ ‘to provide the Lord with.’ A people prepared, or, ‘a people fit to be used’ (Chinese Union Version). If the aim of preparation has to be made explicit, one may say, .’.. prepared for (or, to serve) him.’ — People may have a generic meaning, ‘several persons,’ or it may refer, as it does here, to a particular political and/or racial entity, such as Israel, and then has been rendered, ‘nation’ (see on 7.5), ‘race,’ ‘tribe,’ ‘the hundred (sur)names’ (Chinese Union Version, traditional for the totality of the Chinese people), or a term for the collective citizens (Lü Zhenzhong). When that entity is seen in its relationship to a ruler or overlord, one may have to say, ‘the subjects.’ When that ruler is God, the same rendering often can be used (as is done here in Balinese), or a specific term designating a people as a religious community, e.g. the followers of a prophet or the worshippers of a god (Bahasa Indonesia). In some cases the term is used to indicate the common people in contrast to their leaders, see on 7.29.
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.