now: at this very moment, the present instant as opposed to the past or the future
This little adverb pins a statement to the present moment. It answers the question when with the tightest possible reply: right now, at this instant. Often it carries a flavor of immediacy that plain "now" in English can blur, the sense of "just now" or "only now," a moment freshly arrived. When a girl has "just now" died (Matthew 9:18) or a man born blind can "now" see (John 9:25), the word marks the sharp edge between how things were and how they suddenly are.
Greek has a second common word for "now" (νῦν), and comparing them sharpens what this one does. The broader word points to the present period or the present state of affairs, the way we say "now that things stand as they do." This word is narrower and more pointed: it fixes the present as a precise instant, the very moment of speaking or acting. The difference is real but small, and English usually flattens both to a single "now," which is why a reader rarely needs to worry about it.
The same core moment can be looked at from either side, and the New Testament writers do this with a preposition. Paired with the word for "from," it becomes "from now on," treating this instant as the starting line for everything that follows (Matthew 26:64). Paired with the word for "until," it becomes "until now" or "up to the present," treating this instant as the finish line of a stretch of time that has been building (John 5:17, 1 Corinthians 15:6). In every case the word itself still means the present moment; the preposition supplies the direction.