Question Restatement
The question seems to be asking:
- what does ὁ χρηματισμός mean in Romans 11:4?
- why did Paul make that word choice, if any
Response
Apparently Paul coined a good many words in the NT and did not coin the word χρηματισμός. Other extant usages of the word vary but this usage seems to be what Paul has in mind:
- of an oracle, give a response to those who consult it, LXX Je.33(26).2, al., D.S.15.10, JAJ11.8.4, Plu.2.435c, Porph. Abst.2.48;
δι’ ὕδατος Iamb.Myst.3.11; of gods, give ear to, χ. τοῖς εὐχομένοις
Luc.Pseudol.8:—Pass., receive an answer, warning, in NT of divine
warnings or revelations, Ev.Matt.2.12, etc.; ὑπ’ ἀγγέλου Act.Ap.10.22;
ἦν αὐτῷ κεχρηματισμένον a warning had been given him, Ev.Luc.2.26; χ.
ὑπὸ δαιμονίων καὶ φαντασίας εἰδώλων Vett.Val.67.5.
http://stephanus.tlg.uci.edu/lsj/#eid=117634&context=lsj&action=from-search
This word is used also in Jeremiah 26:2 LXX where the LORD tells Jeremiah to relate everything he commands him to say and to not omit even a single word:
NET Bible Jeremiah 26:2 The Lord said, “Go stand in the courtyard of
the Lord’s temple. Speak out to all the people who are coming from the
towns of Judah to worship in the Lord’s temple. Tell them everything
I command you to tell them. Do not leave out a single word!
LXX Jeremiah 26:2 οὕτως εἶπεν κύριος στῆθι ἐν αὐλῇ οἴκου κυρίου καὶ
χρηματιεῖς ἅπασι τοῖς Ιουδαίοις καὶ πᾶσι τοῖς ἐρχομένοις προσκυνεῖν ἐν
οἴκῳ κυρίου ἅπαντας τοὺς λόγους οὓς συνέταξά σοι αὐτοῖς χρηματίσαι
μὴ ἀφέλῃς ῥῆμα
Paul, I believe, is likening the interaction of Elijah with God between the time that he mentions his predicament to the time he receives a response to consulting an oracles. It seems to me that Paul wants to "color" Elijah's exchange with God with language of "consulting an oracle".
Why? Because he understands that the one who appeared to Elijah was not God himself but rather his "go-between" aka ὁ χρηματισμός aka "the oracle" aka "the one who delivers χρησμοί ("divine messages/predictions/mysteries")", the angel:
NIV 1 Kings 19:
5Then he lay down under the bush and fell asleep.
All at once an angel touched him and said, “Get up and eat.” 6He
looked around, and there by his head was some bread baked over hot
coals, and a jar of water. He ate and drank and then lay down again.
7The angel of the Lord came back a second time and touched him and
said, “Get up and eat, for the journey is too much for you.” 8So he
got up and ate and drank. Strengthened by that food, he traveled forty
days and forty nights until he reached Horeb, the mountain of God.
Continuing, with the angel acting as oracle, a divine prediction of a particular denouement is given to Elijah. I suspect that this is an example of or runs parallel to the idea of a god communicating a mystery to someone with the dire warning that they must not reveal the secret to anyone on pain of indescribable pain and suffering. Here the mystery is that God has 7000 remaining adherents.
9There he went into a cave and spent the night.
And the word of the Lord came to him: “What are you doing here,
Elijah?”
10He replied, “I have been very zealous for the Lord God Almighty. The
Israelites have rejected your covenant, torn down your altars, and put
your prophets to death with the sword. I am the only one left, and now
they are trying to kill me too.”
11The Lord said, “Go out and stand on the mountain in the presence of
the Lord, for the Lord is about to pass by.”
Then a great and powerful wind tore the mountains apart and shattered
the rocks before the Lord, but the Lord was not in the wind. After the
wind there was an earthquake, but the Lord was not in the earthquake.
12After the earthquake came a fire, but the Lord was not in the fire.
And after the fire came a gentle whisper. 13When Elijah heard it, he
pulled his cloak over his face and went out and stood at the mouth of
the cave.
Then a voice said to him, “What are you doing here, Elijah?”
14He replied, “I have been very zealous for the Lord God Almighty. The
Israelites have rejected your covenant, torn down your altars, and put
your prophets to death with the sword. I am the only one left, and now
they are trying to kill me too.”
This is the response that Paul refers to:
15The Lord said to him, “Go back the way you came, and go to the
Desert of Damascus. When you get there, anoint Hazael king over Aram.
16Also, anoint Jehu son of Nimshi king over Israel, and anoint Elisha
son of Shaphat from Abel Meholah to succeed you as prophet. 17Jehu
will put to death any who escape the sword of Hazael, and Elisha will
put to death any who escape the sword of Jehu. 18Yet I reserve seven
thousand in Israel—all whose knees have not bowed down to Baal and
whose mouths have not kissed him.”
This, in my analysis represents the following:
- the term in question is from the domain of "consulting of oracles"
- oracles delivered a divine secret message via his angel
- hence Paul's use of the jargon for the "inquiring of the oracle" - the angel was the deliverer of the message, but from God.