1st para- At a turning of life mujhe laga ki we should leave past behind and phir move forward, play a new music in my heart which means ki basically change or detach myself from something old to move towards the future.
2nd para- the love from which we get the light and hope (positiveness or same feeling), why don't we sing that song.
3rd para- What I like today, may change tomorrow, when old leaves shed, in place of it grows a new bud on some branch of a dry tree.
4th para- I don't want what I've got, why don't I get that which I want?
Basically means ki move on from old stuff cause when you leave something old only then something new comes to your life and that you don't want what you have cause you didn't get what you want.
KISI KO SMAJ AYE MUJHE BHI BATANA