Here we get the adjectives "motionless" and "forgetful" to describe the word "where," and then "shining" to describe "here."
The speaker may be getting across the idea in a weird way, but it seems like what he's getting at is a pretty familiar. He's saying that his father really made the most of each moment. He brought things to life wherever he went.
How did we come up with this?
Well, "motionless" kind of reminds us of something that's dead or at least sedentary.
And then you've got "forgetful," which makes us think of something that's just not with it.
Then those words are used to describe "where," which makes us think of somewhere distant, or at least a vague place.
So, we've got some vague place that doesn't move and just isn't with it. In the next line, though, we're told that all the father has to do is look at terrible "where," and turn it into a "shining here."
It's bright. It's alive. It's present.
The idea actually totally reminds us of that singing-morning-from-night business in the first stanza.
that if(so timid air is firm) under his eyes would stir and squirm
The speaker continues that same figurative thought from the previous two lines and confirms our suspicions about the meaning of this stanza.
The father can look at air that is "firm," which reminds us of the motionless thing before, and with only a glance he can make it "stir and squirm."
"It's alive!" says Dr. Frankenstein... and the speaker's father, apparently.
This is a guy that brings life and an excitement for living wherever he goes.