Why does earth's distance from the sun change?

Thanks for the depiction. 's distance CS = ae from center C is 1 in 60 of the semi-major a. So, for orbit on an A4 paper, S will be quite close to C.

e = 0.01671. CS/a = 0.01671. Also, minor axis b is 0.99986a. If the orbit is drawn to scale on A4 paper, it will appear as a circle. Of course, some elongation is necessary to show what it is, an ellipse.