a small word that draws a conclusion from what has just been said, like "so," "then," or "therefore," with a tone that ranges from cool logical consequence to startled realization.
ἄρα (transliterated ara) is the New Testament's subtler word for "therefore" or "then." It marks a conclusion the speaker draws from the line of thought just completed. There is a heavier and more common word that also means "so" or "therefore," οὖν (oun); but where οὖν points to a conclusion forced by outside facts, ἄρα points inward, to a consequence the speaker personally sees. The classic way scholars put it is that ἄρα looks to the inner reason while οὖν looks to the outer one.
This inward quality accounts for the word's range. Most of the time it marks a cool logical step, the kind of move a debater makes at the end of a chain of reasoning. Paul uses it this way constantly, especially in Romans, where it knits his argument together. But the same inward quality also gives it a flavor of sudden realization in narrative and conversation: ἄρα can signal fresh perception, a dawning awareness that something is the case, the sense of "so it turns out." Acts 21:38 and Acts 11:18 are the clearest New Testament examples of this older, more emotional use.
Paul's doubled form ἄρα οὖν ("so then"), found twelve times in his letters and nowhere else in the New Testament, is his personal signature for closing off a paragraph or pivoting from a point of doctrine to a practical command. None of its occurrences appear in the Greek Old Testament. This pairing is Paul's own Greek, not something he inherited from the Bible's earlier Greek.
In the older, stricter form of the language, ἄρα could never stand first in its sentence; it always followed another word. The everyday Greek of the New Testament era relaxed that rule, and Paul takes full advantage: he regularly opens a sentence with ἄρα or ἄρα οὖν to make the conclusion audible and emphatic. The same freer usage shows up in ordinary private letters of the period, confirming that this is normal everyday Greek, not a literary peculiarity.