A few weeks ago, I told you the story of Fanaa, where blind girl Zooni, fell in love with Rehan, who faked his death in a terrorist attack.
When they saw each other again, she had gained her sight (because he helped her get the operation) and had his child. He did not tell her who he was, because he did not want her to know the reason why he had to leave her all those years ago. To do that, would mean he would have had to admit to the kind of activities that he was involved in.
When she finds out that the injured soldier (terrorist in hiding) who came to her door, was Rehan and they fall in love again and get married (he doesn't tell her about his real past), and this song is played:
Mere Haath Mein
It's a lovely song, but the lyrics don't translate well in English, in summary, their lives are complete when their hands are together, and now they have no use for anything else in life - they are content just being with each other.
Just enjoy the music.