What is the poem about if I could catch a rainbow

If I could catch a rainbow,
I'd do it, just for you,
And share with you it's beauty,
On days when you feel blue.

If I could, I'd build a mountain,
You could call your very own,
A place to find serenity,
A place to be alone.

If I could take you troubles,
I would toss them in the sea,
But all these things, I'm finding,
Are impossible to me.

I cannot build a mountain,
Or catch a rainbow fair,
But let me be what I do best,
A friend who's always there

I hope this helps