It refers to life. It’s a phrase that is quite popular with poets and lyricists.

This moment is unique in time, and we can’t revisit it. Even if you come back to the same place, return to the same path, “things” will be different.

The meaning of Eva Rose York’s I Shall Not Pass This Way Again is that life is precious, and to live every moment to the fullest, and at every opportunity, help others in their lives so that you will be well remembered.

Stephan Grellet’s poem is so direct, it needs no interpretation and means pretty much the same thing.

James Seals song has the same meaning with the inclusion of a romantic partner:

So, I wanna laugh while the laughin’ is easy. I wanna cry if it makes it worthwhile.

We may never pass this way again, that’s why I want it with you.

‘Cause, you make me feel like I’m more than a friend.

Like I’m the journey and you’re the journey’s end.

We may never pass this way again, that’s why I want it with you

Once and only once I pass;

If a kindness I may show,

If a good deed I may do

For a suffering fellow man,

Let me do it while I can.

No delay, for it is plain

I shall not pass this way again!

~ unknown ~

the author makes his/her intent clear in

verse two.

seeing whats awaiting at the end of life.

the author is determined in

being a compassionate bein

while there is time left to be so.