v15 προσδοκωντος (προσδοκαω) gen. pres. part. "were waiting expectantly" participle with the noun του λαου, "the people" both being genitive absolute, usually forms temporal clauses but a causal clause seems more likely here. The sense is that the crowd which has come out to John, is now filled with messianic expectation due to his preaching and needs instruction.
διαλογιζομενων (διαλογιζομαι) gen. pres. part. "they were [all] discussing” εν "in [their hearts]" – they were reflecting on John’s sermons.
μηποτε "perhaps” usually points to a negative conclusion, i.e. they knew John was not the messiah but translated as expressing doubt (particularly using the optative of to-be).
v16 λεγων (λεγω) pres. part. [John answered] saying πασιν to all - given the context, John is addressing all in the crowd being baptized.
μεν ...... δε "on the one hand, on the other" – a comparative idiom – on the one hand I baptize on the other one is coming that is mightier than εγω "even I" (emphatic). John tacitly claims authority to forgive sin through baptism but the power of the Messiah will be greater.
βαπτιζω pres. "I baptize" - present tense = ongoing action “I continue to baptize”.
υδατι (ωρ ατος) dat. "with water" –instrumental dative (emphatic) so, "I baptize only or merely with water."
ο ισχυροτερος comp. adj. "one more powerful". μου gen. pro. "than me” an ablative of comparison who is an ικανος adj. "the insignificant one" by comparison!
λυσαι (λυω) aor. inf. "to loose” - an epexegetic infinitive, explaining the adjective
των υποδηματων (α ατος) gen. "[the straps] of [whose] sandals" – servant’s work.
αυτος "he" – Emphatic, so ONLY he.
πνευματι αγιω/ και πυρι "the Holy Spirit and [with] fire" - whatever that means – a singular sense is possible, eg. " a purging (cleansing) Spirit", or " holy fire of judgment", but the messiah will "immerse” in the sense of βαπτιζμο, which at root means to overwhelm with both Spirit (regeneration) and fire (tribulation).
v17 το πτυον (ον) "[his] winnowing fork" - used to separate chaff from grain by casting into the air on a windy day; an image of judgment.
διακαθαραι (διακαθαιρω) aor. inf. "to clean out thoroughly”- an infinitive expressing purpose "in order to cleanse."
συναγαγειν (συναγω) aor. inf. "to gather" – an infinitive expressing purpose, "in order to gather."
κατακαυσει (κατακαιω) fut. "he will burn up" πυρι ασβεστω dative "with a fire that cannot be extinguished”; likely an allusion to the rubbish dump outside Jerusalem often used to visage judgment, cf. Isa.34:10, 66:24.
v18 παρακαλων (παρακαλεω) pres. part. "John was admonishing” reflecting his stern message.
ευηγγελιζετο (ευαγγελιζω) imperf. "preached the good news" - usually a technical term referring to gospel preaching, so "evangelizing", but here, because the content is nothing like later gospel messaging, more likely in the sense of just communicating, i.e. "he spoke his piece to the people".
v19 ελεγχομενος (ελεγχω) pres. pas. part. "when John rebuked" Herod because he had relations with Herodias his brother's ex-wife. Herodias was initially married to Herod, (son of Herod the Great and Mariamne) but then divorced (?) him and married his younger brother (or not – either would have been cause for scandal) Herod Antipas, son of Herod the Great and his second wife, Malthake.
v20 προσεθηκεν (προστιθημι) aor. "Herod added" – an idiom meaining; on top of everything else – so Herod's biggest crime was to attempt silence God’s prophet and hence God. Herod plays the role of an OT king. Luke now ends his historical aside and returns to the narrative.
v21 εγενετο (γινομαι) aor. it came to pass.
εν τω βαπτισθηναι (βαπτιζω) aor. pas. inf. "when [all] were being baptized" - the articular infinitive forms a temporal clause. Note the sequence with the action that follows: "Jesus was baptized", "was praying", the "heaven opened".
απαντα τον λαον "all the people" - "all" obviously does not mean everyone, but does serve to indicate the success of John's ministry. While Mark indicates that only Jesus witnessed what followed, Matthew tells us at least John saw it but Luke leaves us guessing. It is unlikely that the crowd witnesses what follows, but then there remains the obvious question, if no one saw it, who is Luke (and Mark and Matthew) sourcing?
βαπτισθεντος (βαπτιζω) gen. aor. part. "[Jesus] was baptized" - Jesus' willingness to submit to John's baptism has been an ongoing issue in New Testament commentaries. Neither Mark nor Luke see a need to apologize for his willingness to be baptized by John (Matthew includes an aside addressing the issue i.e. that the baptism was done to ‘fulfil all righteousness” - whatever that means) nor do they see any need to explain the paradox of the one who baptizes with the Spirit being baptized by the one who baptizes “merely” with water. Jesus' baptism rather, followed as it is by the temptation in the wilderness, reflects an Exodus typology. Jesus, as Israel responds to the divine call to the wilderness (where Israel's sonship was also restored), then passes through the water into the wilderness. The Exodus motif is redemptive and although unstated in the gospel accounts probably central. So, Jesus, as faithful Israel, does what Israel must do, step out in faith to play the part of the repentant sinner, and as faithful Israel is declared God’s beloved. As Barth puts it, in his baptism Jesus becomes "the great Sinner who repents."
προσευχομενου (προσευχομαι) gen. pres. part. "was praying" – a genitive absolute participle in the present tense, indicates that Jesus' prayer continues as the heavens open.
τον ουρανον (ος) "heaven" - possibly Luke means "the sky parted", or “God's domain”.
ανεωχθηναι (ανοιγω) aor. pas. inf. "was opened" - infinitive serves as the subject of the verb εγενετο "it came to be" an apocalyptic revelation motif, cf. Ezk.1:1
v22 καταβηναι (καταβαινω) aor. inf. "descended" – also an infinitive functioning as the subject of the verb εγενετο. The Holy Spirit is not usually described as "coming down" but once again the Exodus typology is possibly at work, "the Holy Spirit came down from the Lord and led them", Isa.63:14, LXX.
σωματικω ειδει dat. "in bodily form" – these words indicate approximation rather than incarnation. The words are not in Mark so Luke is probably stressing the fact that the Holy Spirit takes "the appearance of a dove" i.e. "dove-like."
περιστεραν (α) "a dove" actually pigeon but that doesn't quite have the same ring! The "dove" doesn't represent the Holy Spirit, it is the Holy Spirit, Luke describes this incident as a theophany, like the burning bush. In this vision, Jesus sees the Holy Spirit as dove-like, it comes to Jesus, the representative Israel, sets him apart, equips him for service, and sets him on the journey. Like the baptism itself, the descent of the Spirit is part of the inauguration of the messianic mission.
φωνην (η) "a voice" - again a theophany. In apocalyptic literature, God is described as speaking, usually for the purpose of instruction, here for a commissioning.
συ "you" - Emphatic - Jesus is being singled out, over John.
ο υιος μου "[are] my Son" - designation, "the son of mine", used as a title for messiah, in the Old Testament also of a king, nation, even angels ("sons of God" in Job). The term "beloved Son" may incorporate the idea of Jesus' unique relationship but here more likely identifies Israel as God's chosen ones represented by the messianic king. This first part of this quote is from the coronation liturgy found in Psalm 2:7.
ο αγαπητος adj. "the one I love" - carries the sense of a particular, or uniquely set-apart association, so "my one and only son dearly loved", even "my only son" but at root again expresses the unique relationship the messiah has with God.
ευδοκησα (ευδοκεω) aor. "I have come to delight” "well pleased" is borrowed from Isaiah 42:1 but many scholars follow an alternate reading which just quotes from Psalm 2:7, "You are my son, today I have begotten you." Isaiah 42:1 from the “ordination liturgy” of the suffering Servant.