A discussion site for Atisha's Lamp for the Path to Enlightenment
This verse refers to persons who aspire to attain enlightenment for themselves alone, that is, who aspire to become arhats or solitary buddhas (pratyekabuddhas). Traditionally, the path for becoming an arhat is to meditate on the sixteen aspects of the four noble truths. And to become a solitary buddha, one meditates on the twelve links of the chain of conditioned production (pratiyasamutpadda). Of course, there's much more to the path than this simple summary. This path is greater than the lesser path because it puts a final end to suffering for the person who pursues it, unlike the lesser path, which only results in temporary happiness. But it is lesser than the greater path, since this benefit is only for a single individual. So it is called the middling path.