Linker used in pronoun in this song lyric: nating

[Al-Indunisiy]

Dati-rati sabay pa nating pinangarap ang lahat.
"Back then, we dreamed everything together"

I know that 'pinangarap' is object-focused verb so 'natin' (the subject) is marked as indirect case and 'lahat' (the object) is marked as direct case. What I don't understand is why 'natin' is given the linker thus becomes 'nating'?

 

[DotterKat]

The linker -ng at the end of natin simply enforces the relation between the words natin and pinangarap. In some instances, as in this one, you can drop the -ng linker with no serious grammatical consequence.
The noticeable difference will be in spoken Tagalog. Nating pinangarap flows more smoothly out of the mouth than natin pinangarap.
In this instance, the sound articulators most involved are the tongue and hard palate. When you say nating pinangarap, the -ng linker at the end allows separation of the tongue from the hard palate which makes articulating the following syllable pi- easier to form and thus allow more fluid articulation. This is especially important in poems and songs.
As in other languages, repeated verbal practice will reveal what formulation will sound right. In situations such as this, grammatical rules are flexible and tend to yield to exigencies of verbal fluency.