Knowledge is the Light from our inner Self, through it we see and perceive everything.
Knowledge is reflected in the mind like the sunlight in the water. Reflection is the understanding.
As a still and clear water reflects light clearly, a quiet mind that recognizes itself pure has a clear understanding of the Truth given by Knowledge.
The understanding that you get from these words is the reflection of their light in the own mind. If this understanding creates ideas, it means that the mind is still restless with thoughts that disturb it; like small waves on the water created by wind (thoughts) that reflects flashes (ideas) of light.
Into a quiet mind the understanding is similar with the light of knowledge.
The mind has the power to soothe itself, such as the water settles and clears up when the weather is calm.
By trying to focus the mind only in the light (truth) of understanding, that understanding becomes brighter, which also shows that the mind becomes peaceful.
In a very still and clear water we see clearly the light and our own image; the same it is into a peaceful and serene mind, the understanding is identical with the truth and we recognize our inner Self whose light is the Knowledge ("The light that enlightens every person").