Exegesis:

Main clause to the two absolute genitives of v. 15 (prosdokōntos tou laou ‘as people were in expectation,’ and dialogizomenōn pantōn ‘as all were wondering’) is the first clause of v. 16, apekrinato … Iōannēs, ‘John answered.’ The relationship of the two absolute genitives to one another depends on the interpretation of the first one, see next note.

(V. 15) prosdokōntos de tou laou ‘as people were in expectation.’ de, which has not been translated, marks the beginning of a new development. The participle prosdokōntos which has no object, is best understood in an absolute sense as e.g. in Revised Standard Version. People were “in a great state of expectation” (Phillips), because of John’s message. The clause describes the result of John’s preaching, cf. An American Translation, “as all this aroused people’s expectations”. Then laos does not refer to the people of Israel in general but to the people that came out to listen to John. For prosdokaō cf. on 1.21.

dialogizomenōn pantōn ‘as all were wondering,’ describes a further and more specific result of John’s preaching; pantes refers to the same people as laos in the preceding clause. For dialogizomai cf. on 1.29.

en tais kardiais autōn ‘in their hearts,’ or, “in their minds” (Translator’s New Testament), or, “inwardly” (Phillips).

mēpote autos eiē ho Christos ‘whether perhaps he was the Messiah.’ autos is unemphatic ‘he,’ referring back to John’s name in the preceding clause. The optative eiē has no special function. Instead of ‘the Messiah’ Revised Standard Version and several other translations have “the Christ”, a transliteration of the Greek rendering of the Hebrew word. This must be regarded as a second best rendering.

(V. 16) apekrinato legōn pasin ho Iōannēs ‘John answered saying to all,’ cf. on 1.60.

egō men hudati baptizō humas ‘As to me, I am baptising you with water.’ egō is emphatic and men suggests that a contrast is to follow. hudati ‘with water,’ instrumental dative. The present tense baptizō is habitual, ‘I practise water-baptism.’

erchetai de ho ischuroteros mou ‘but the one who is mightier than I is coming.’ de corresponds to men in the preceding clause but the clause which corresponds materially with it (‘he will baptise you with the Holy Spirit and with fire’) does not come until its subject, i.e. the mightier one, is properly identified in his relationship to John. The clause introduces the mightier one as someone who is known, though no previous reference has occurred.

ischuros ‘strong,’ ‘mighty.’

hou … autou ‘whose … of him.’ The relative pronoun at the beginning of the clause and the personal pronoun at the end both go with ton himanta tōn hupodēmatōn ‘the thong of the sandals’ and are therefore to be rendered only once. This is probably a semitism but also not unknown in Greek.

hikanos of things ‘adequate,’ ‘considerable,’ of persons ‘fit,’ ‘competent,’ here with the connotation ‘worthy for something,’ and followed by a complementing infinitive.

lusai ton himanta tōn hupodēmatōn ‘to untie the thong of the sandals.’ This was considered to be the task of a slave.

luō ‘to loose,’ ‘to untie,’ ‘to set free.’

himas ‘thong,’ or ‘strap’ on sandals.

hupodēma ‘sandal,’ “a leather sole that is fastened to the foot by means of straps”.

autos humas baptisei en pneumati hagiō ‘he will baptise you with Holy Spirit.’ autos ‘he’ is emphatic and contrasts with egō at the beginning of the verse. humas ‘you’ does, of course, not imply that this baptism will be limited to those who have previously received John’s baptism with water, just as humas in the first clause of this verse does not mean that John only baptised those to whom he talked at the moment.

en pneumati hagiō ‘with,’ rather than ‘in the Holy Spirit.’ The phrase ‘to baptise with the Holy Spirit,’ occurs only in connection with, and contrast to, John’s baptism with water (Mt. 3.11; Mk. 1.8; Lk. 3.16; Jn. 1.33; Acts 1.5; 11.16) and not as an independent expression. It is therefore best understood as an analogy to the baptism with water and to be interpreted along the same lines as that phrase.

kai puri ‘and with fire.’ This addition also in Matthew but not in Mark. There are two interpretations: (1) the fire is the fire of judgment (Klostermann, Zahn) because of the mentioning of the fire in vv. 9 and 17 both in a picture that refers to the coming judgment; (2) the fire is the fire of purification (Plummer, Lagrange). Interpretation (1) is preferable. This implies a disjunctive relationship between pneuma hagion and pur.

Translation:

It is often better not to render v. 15 as a subordinate clause, but as one separate sentence, formed by two co-ordinated clauses with or without connective, or as two such sentences.

The people, here virtually the same as ‘the crowd.’

Were in expectation, or, if the expression requires an object, ‘were expecting something,’ ‘were believing that things of importance would come to pass’ (Kituba).

All men, or, “they … all” (An American Translation), ‘everyone (amongst them),’ referring to the subject of the first clause, cf. also, ‘the multitudes,’ partly repeating ‘the multitude of people (i.e. the crowds)’ (Lü Zhenzhong).

Questioned in their hearts, or, ‘inquired in their minds’ (Dravidian languages), ‘were asking-themselves in heart of them’ (Kituba), the qualifying word or phrase being required to show that no discussion with others is meant; or again, ‘wondered (lit. guessed and doubted)’ (Chinese Union Version), ‘were-thinking’ (Marathi, Manobo), without such a qualification.

Concerning John, whether perhaps he were the Christ may have to be restructured, e.g. .’.. whether perhaps J. were the Messiah,’ or, if the verb is to be followed by direct discourse, “Is John (or, this man, or, he) perhaps the Messiah?”, “What? Might he be Christ?” (Marathi).

(V. 16) Answered. Revised Standard Version‘s rendering of Gr. apokrinomai by a form of ‘to answer’ here (and in 5.22, 31; 7.40a; 8.50; 9.49; 11.45; 13.15) is rather unidiomatic because it does not introduce a person’s reaction upon a request or statement that has been addressed to him. As a rule it is preferable in these cases to shift to another verb, e.g. ‘to speak up,’ ‘to start speaking,’ ‘to address’; or ‘to interpose’; or a combination of ‘to say/ speak to’ with such expressions as ‘on his part,’ ‘to this,’ ‘again,’ ‘then,’ ‘thereupon,’ ‘but,’ ‘however,’ as required by the context; hence here e.g. ‘But John said to them.’ Such renderings have been used by Revised Standard Version itself for similar occurrences of apokrinomai (e.g. 1.60, cf. also 13.14; 17.17, 37; 22.51), but some other translations have used ‘to answer/reply’ for nearly all occurrences even though decidedly unidiomatic in the language concerned. Their example is not to be followed.

I, or more emphatically, ‘as for me (lit. to me), I’ (Kituba, similarly Kannada), ‘I indeed’ (Marathi).

He who is mightier, etc. is to be applied to the Messiah, although his name is not explicitly mentioned; hence in the references to his person and acts in vv. 16f the use of honorifics may be required in languages like Balinese and Javanese. — Comparative forms of adjectives may not be available in the receptor language. Then it is usually possible to circumscribe the comparison by ‘he surpasses me (or, he is ahead) in might/power,’ or to use a positive-negative contrast, ‘he is (really) mighty, I am not mighty.’ For mighty, or, ‘powerful,’ cf. on “power” in 1.35.

The function of the clause the thong of whose sandals I am not worthy to untie is to give the measure of the difference in might between John and Jesus; hence, “I am not good enough even to untie his sandals” (Good News Translation), ‘mightier than I so that (or, so much mightier than I that) I am unworthy to untie-for-him….’ — Thong, or, ‘tie,’ ‘straps’; in some cases not rendered by a separate term but implied in the verb for ‘untie.’ Chuukese has to use a descriptive phrase, ‘covering-of his-foot.’ — I am not worthy to, i.e. I have not sufficient worth/value/excellence to. In Trukese, Pohnpeian, and some Indonesian languages one says, ‘it is not fitting that I ….’

With the Holy Spirit and with fire. The rendering of this phrase should be modelled on that of ‘with water,’ where necessary marking a shift from metaphor to simile by adding a clue like, ‘as it were.’ The disjunctive relationship between the two nouns may be suggested by using ‘or’ instead of ‘and’ (Kituba), or expressed more explicitly by saying, ‘some of you with the Holy Spirit, others with fire,’ cf. ‘some of you he will baptise with the H. Sp. and the rest he will baptise with fire’ (Manobo).

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.