A song should take you somewhere... like a little timeshare condo in your head. An instrumental can take you to the door, but a well-written lyric lets you go in, get a beer and lay around in the hammock for a while.

To continue to mix (abuse?) metaphors, writing a song is nothing more than reaching for the proverbial brass ring... I hat it one moment and cling to its skirts like a needy child the next, begging for something just outside my reach.  Like a dog snapping at soap bubbles, I get one and find it's just disappeared and left a funny taste in my mouth -  but once in a while, I get that magic bubble and it opens up a hole in the fence through which, somehow, one single little patch of this untamed universe falls into place and makes total sense to me.