I think people sometimes reach too hard for a singular meaning. The speaker stops to watch woods fill up with snow, feels that pull of beauty and darkness, then remembers he has 'promises to keep.' It's not a riddle about death, though that reading is popular. I see it as a moment of suspension between two kinds of obligation—one to the world of duty and miles ahead, the other to the quiet, deep attraction of simply stopping. That 'lovely, dark and deep' woods isn't necessarily sinister; it's an escape from the harness and the bells. The repetition of the last line feels like a man convincing himself to move on, a mantra against surrender. The significance isn't in decoding what the woods 'are,' but in recognizing that tension itself is the core of a life. I've had drives home where I just wanted to pull over and sit, not for any dramatic reason, just to pause. Frost captures that universal, mundane temptation perfectly.
That 'And miles to go before I sleep' repeated twice changes. The first is factual, the second weighted, like he's trying to believe it. The sleep could be literal rest, or the final sleep. But making it only about death flattens it. It's about all the road left, all the chores, the entire weight of a lifetime before any kind of repose, even a nightly one. The beauty makes the burden sharper. That's the ache.