Verse 17

17.  As the rope,  with its nature not definitely ascertained in the dark,  is imagined to be possessed of the nature of entities like the serpent,  or water line etc;   so likewise is Atman imagined to be all sorts of things.

" As the rope,  with its nature not definitely ascertained in the dark,  is imagined to be possessed of the nature of entities like the serpent,  or water line etc;"

Within the forgetting of Maya,  the light of Absolute knowledge is not seen.  Therefore,  as explained in the previous verse the mind learns and commits to memory a knowledge based on worldly experience.
Here,  with the example of a rope that is temporarily unrecognisable due to a lack of sensory information,  The mind uses it's stored memory of knowledge to fill in the gaps of sensory knowledge.  The result is mind  "sees"  or imagines a long thin snake or a long thin water line.

"so likewise is Atman imagined to be all sorts of things."

"So likewise",  due to our forgetting,  in consciousness,  of Absolute Knowledge as the singularity of Existence our stored memory of sense experiences gives a false reality to the appearance of individual forms.