Oun is an inferential conjunction meaning "therefore," "then," "so," or "consequently." It draws logical conclusions from what has been stated. It appears about 499 times in the NT and is especially common in John and Paul, where careful argument is being built.
Tracking the oun clauses in a passage reveals the logical skeleton of the author's argument. It signals: "given what I just told you, here is what follows." It connects doctrine to life, indicative to imperative.
Romans is the most sustained theological argument in the NT, and its oun constructions are pivotal. The famous "Therefore, there is now no condemnation for those who are in Christ Jesus" (Romans 8:1) draws a sweeping conclusion from everything in chapters 1–7. The oun carries the weight of the entire argument.
Romans 12:1 — "Therefore, I urge you, brothers and sisters, in view of God's mercy, to offer your bodies as a living sacrifice" — uses oun to hinge the practical ethics of chapters 12–16 on the doctrinal foundation of chapters 1–11. Godly living is the therefore of the gospel.
John uses oun as a narrative connector: "So [oun] when Jesus saw her weeping…" (John 11:33). Even in narrative, it creates cause-and-effect flow, showing that Jesus's responses are grounded in real perceptions and compassion.