√ πάλιν — (adverbially) anew, iAdverb
palin: again, anew A resumptive adverb. It ties this promise to the binding and loosing of v. 18 rather than opening a fresh topic, which is why Barnes, Cambridge and Poole all read vv. 19 to 20 as continuing the discipline paragraph.
√ λέγω — properly, to "lay" forth, iVerbPresent Indicative Active1st Person Singular
√ σύ — thouPersonal / Possessive PronounDative 2nd Person Plural
√ ἀμήν — properly, firm, iHebrew Word
amēn: firm, truly Parsed simply as "Hebrew Word": an untranslated Hebrew term carried whole into Greek. Matthew keeps it as a spoken seal on a promise rather than a response to one, and here it stands after "I say to you," so the solemnity falls on the pledge that follows. The word that elsewhere ends Israel's prayers begins the Lord's guarantee about prayer.
√ ὅτι — demonstrative, that (sometimes redundant)Conjunction
√ ἐάν — a conditional particleConjunction
ean: if (conditional particle) With the subjunctive verbs that follow, this is the particle of a real but unfixed case: not "whenever you happen to agree" but "if it should come about that two sound together."
√ δύο — "two"AdjectiveNominative Masculine Plural
dyo: two The number is deliberate and small. Pulpit calls it "the smallest number that could form an association," and JFB sees the low number as the whole point: "by letting it down so low as that number, He gives the utmost conceivable encouragement to union in this exercise." Ellicott hears in it a backward reference to the two witnesses of v. 16, so the pair that confronts a sinner is the same pair that may now pray.
√ ἐκ — literal or figurativePreposition
ek: out of, from among Partitive: two drawn out from among the larger body, not two standing apart from it.
√ σύ — thouPersonal / Possessive PronounGenitive 2nd Person Plural
√ ἐπί — properly, meaning superimposition (of time, place, order, etcPreposition
√ ὁ — the (sometimes to be supplied, at others omitted, in English idiom)ArticleGenitive Feminine Singular
√ γῆ — soilNounGenitive Feminine Singular
συμφωνήσωσινsymphōnēsōsinagreeG4856 √ συμφωνέω — to be harmonious, iVerbAorist Subjunctive Active3rd Person Plural
symphōneō: to be harmonious, to sound together A rare verb, present in only six verses of the New Testament, and the theological centre of the sentence. Because it is aorist subjunctive active, the agreement is a single achieved concord rather than a settled disposition. JFB draws the whole doctrine out of the voice of the word: "not an agreement merely to pray in concert, but to pray for some definite thing," and then "symphonious prayer, the prayer by kindred spirits." Note the honest limit the same lexeme imposes: in Acts 5:9 it names the agreement of Ananias and Sapphira, so concord by itself is no proof of the Spirit.
√ περί — properly, through (all over), iPreposition
παντὸςpantosanythingG3956 √ πᾶς — all, any, every, the wholeAdjectiveGenitive Neuter Singular
πράγματοςpragmatos. . .G4229 √ πρᾶγμα — a deedNounGenitive Neuter Singular
pragma: a deed, a matter, a piece of business Eleven verses only. It is the word for an affair that has to be settled, which is why it sits so well after the offended brother, the two witnesses and the church's verdict. Hebrews 6:18 pairs it with the same numeral as here, "two immutable things," in the context of an oath that secures a promise; 1 Corinthians 6:1 uses it of a suit between believers. The Verifier records both contacts.
√ ὅς — the relatively (sometimes demonstrative) pronoun, who, which, what, thatPersonal / Relative PronounGenitive Neuter Singular
√ ἐάν — a conditional particleConjunction
αἰτήσωνταιaitēsōntai[you] ask forG154 √ αἰτέω — to ask (in genitive case)VerbAorist Subjunctive Middle3rd Person Plural
aiteō: to ask, to request Aorist subjunctive middle. ⚙ The middle can carry the sense of asking with one's own interest in view, which would suit petitioners bringing their own case; but Koine's middle and active of this verb are not always cleanly distinguished, so this reading is offered lightly and should not be made to bear weight. What is certain from the parse is the third person plural: the promise is stated about such a pair, not only to this pair.
γενήσεταιgenēsetaiit will be doneG1096 √ γίνομαι — to cause to be ("gen"-erate), iVerbFuture Indicative Middle3rd Person Singular
ginomai: to come to be, to be generated Future Indicative Middle, third person singular, agreeing with the single "matter" asked. ⚙ Do not press the middle voice here: the future of ginomai is middle in form as a matter of the verb's own morphology, not as a theological signal. What does carry weight is that the verb is not "it will be permitted" or "it will be considered" but "it will come to pass," and that the agent is named only obliquely, para tou Patros, from beside the Father.
αὐτοῖςautoisfor [you]G846 √ αὐτός — the reflexive pronoun self, used (alone or in the comparative G1438 (ἑαυτοῦ)) of the third person , and (with the proper personal pronoun) of the other personsPersonal / Possessive PronounDative Masculine 3rd Person Plural
autos: himself, them "For them." BSB's "for you" is a harmonization with the surrounding second person plurals; the Greek has stepped into the third person. See the divergence note above.
√ παρά — properly, nearPreposition
para: from beside, near Not merely "by" as an agent tag. The preposition puts the answer's origin at the Father's side, so the granting is pictured as something handed out from where He is, which is the same picture Gill draws when he notes that the petitioners are "here on earth, and at such a distance from heaven, from whence their help and assistance come."
√ ἐγώ — I, mePersonal / Possessive PronounGenitive 1st Person Singular
√ ὁ — the (sometimes to be supplied, at others omitted, in English idiom)ArticleGenitive Masculine Singular
√ πατήρ — a "father" (literally or figuratively, near or more remote)NounGenitive Masculine Singular
patēr: father JFB fastens on the possessive: "Not for nothing does He say, 'of My Father', not 'YOUR Father'." The answering authority is reached through the Son's own relation to the Father, which is why v. 20 can immediately explain v. 19 by naming the Son's presence rather than the Father's. Gill adds the practical reach of the same clause: "with whom nothing is impossible."
√ ὁ — the (sometimes to be supplied, at others omitted, in English idiom)ArticleGenitive Masculine Singular
√ ἐν — "in," at, (up-)on, by, etcPreposition
οὐρανοῖςouranoisheavenG3772 √ οὐρανός — the skyNounDative Masculine Plural
ouranos: the sky, the heavens Dative plural. Matthew's standing idiom, and here structurally load bearing: the verse is built as earth (v. 19 word 11) answered from the heavens (word 27), with the Father named between them. The two spheres that v. 18 bound together by decision are here bound together by prayer.