Understanding the game loop

So I’ve been using the game loop below for most of the games I’ve made and as I was just going through it I found there is one part I’m having trouble
trying to understand, specifically the line just below.

delta += (now - lastTime) / nanos; 

I understand we are finding the time difference and adding it to the delta variable but I don’t understand why we are then dividing it by the nanos variable (1000000000 / 60). I pasted the full game loop below.

 long lastTime = System.nanoTime(); 
			final double nanos = 1000000000.0 / 60.0; 
			double delta = 0;
			int frames = 0;
			int updates = 0;
				long now = System.nanoTime(); 
				delta += (now - lastTime) / nanos; 
				lastTime = now; 

				 while(delta >= 1){

If anyone could help me by explaining whats happening on the line I pointed out, it would be very appreciated. Thanks!