The line in the composition in question aims to take the look through the composition. Going from left to right, the line leads us to look up and down until we get to the brand name for the line representation: The cellar. The line in this composition drives the viewer's eye.
The line in this composition leads the eye from the top of the picture to the bottom. It represents a staircase and is meant to take the eye from the top down the where the text is written. The text is the main focus of the picture and is what your eye is supposed to be attracted to. The line enables your eye to do that.
