Thread: I walk the line

There is a song which is played a lot on Russian radio: Laurent Wolf remix for "I walk the line" by Johnny Cash.

What does "I walk the line" mean in this song?

Originally Posted by Johnny Cash in I Walk the Line

I keep a close watch on this heart of mine
I keep my eyes wide open all the time.
I keep the ends out for the tie that binds
Because you're mine,
I walk the line

I find it very, very easy to be true
I find myself alone when each day is through
Yes, I'll admit I'm a fool for you
Because you're mine,
I walk the line

As sure as night is dark and day is light
I keep you on my mind both day and night
And happiness I've known proves that it's right
Because you're mine,
I walk the line

You've got a way to keep me on your side
You give me cause for love that I can't hide
For you I know I'd even try to turn the tide
Because you're mine,
I walk the line