1.41. When the agitations of the mind are under control, the mind becomes like a transparent crystal and has the power of becoming whatever form is presented. knower, act of knowing, or what is known

If there any Sutras that you should pay attention to, it's this one. It's the most important Sutra in book one until I say something otherwise, which I'm sure I will. I will break this one down into it's constituent parts because it contains a lot of esoteric information. The Fortress of Mindful Solitude

When the agitations of the mind are under control

All attachments to matter cause agitations in consciousness and drag it willing or unwilling in a certain direction. The agitations of the mind are called Vrittis. I don't know why water makes such a good metaphor for things Yoga related. I don't even like swimming or boating. Anyway, going back to my reference on the nature of thought in my post "Sutras 1.5 - 1.11: What is Thought?" I used a pool of water looking at the surface of the moon as a metaphor for the way the undisciplined mind perceives reality. Now to read that, I'll wait... Good for you smart Alek, you skipped it! The stillness of the water is called Vritti Nhirhodah, or stillness of thought. Practice will get you to this stage of awareness.

the mind becomes like a transparent crystal and has the power of becoming whatever form is presented,

Now that your mind has been stilled, it becomes clear. Now you get to go back and read my post on loosing your marbles. The crystal is like the glass jar. The Yogi then uses this clarity to focus on the object of meditation, which is covered under my posts about My Flav.

knower, act of knowing, or what is known

So here we have one of the holy trinities in Yoga. The essence of you is the knower, which is separate from the action of knowing something, which is conscious projection on to the object of what is known. Like I spoke about in my Cycles of Life posts, much of the logic in yoga runs in circles. We first have to pull apart everything in the mind, to then understand it, to then get rid of it, only to put what is left back together to understand the whole.