The song's engine is a paradox that sounds like a typo and is the whole truth of it. Saans mein teri saans mili toh mujhe saans aayi: when my breath met your breath, then breath came to me. The claim is that she was not breathing before, or at least not in the way that counts, and that the meeting was the first proper breath of her life. Urdu has two words for this and the song uses both: saans, the breath, and rooh, the soul, and the second passage's line, rooh ne chhu li jism ki khushbu, the soul touched the fragrance of the body, does the same work one level up. Not breath meeting breath. Soul meeting scent.
The second passage is the surrender, and it is Gulzar at his most relaxed. How long can anyone keep their wits about them. If the senses fly off, let them fly. When did the heart ever walk a straight road. If the road turns, let it turn. The passage is a licence issued to the heart, and the closing lines give the reason: sinking into your thoughts, loneliness starts to feel good, achhi lage tanhaai. It is the quietest paradox in the song and the most personal: the loneliness is no longer lonely.
The third passage is the film's part, the woman's part, and it is the one with the questions in it. If the night is spent in your arms, the morning feels weightless, halki. And then the question that the whole song has been building to: have you started living in my eyes, why does everything keep welling up, chhalki-chhalki. The eyes are doing the thing eyes do when a person is finally being seen. The passage ends with the request that closes the song: touch me again and speak. Meri qasam kya khaayi: what oath did you take, on my name, that made you this. The beloved's touch and voice are being asked for as proof, one more time.
The two recordings say the same words in two moods. The full song is the meeting itself, with Mohit Chauhan and Shreya Ghoshal trading the passages. The reprise is Shreya alone, and alone the same words become the memory of the meeting rather than the meeting. Jab Tak Hai Jaan was Yash Chopra's last film, and the song is one of the last great ones his name was attached to.