Lights& Vessels; Inside & Out: 2

The purpose of Creation is for man to understand and cleave to Hashem. This understanding is referred to as אור, light. The entirety of the body of the person contributes to his minds ability to achieve this comprehension. They are the כלים, vessels, which facilitate the assimilation of the light.
There are two types of כלים. The limbs of a person serve him to achieve these comprehensions. So too, all other aspects of Creation work to this end as well. The distinction is that a person's limbs are direct contributors to a person's serving Hashem, whereas everything else does so in an indirect manner and are more distantly connected to the person's ability to serve Hashem.
This serves as a way to understand the distinction between the inner and outer vessels. Those which are direct are referred to as the inside. The indirect ones are the outside.

Lights& Vessels; Inside & Out: 1

We will begin this section by offering some definitions of Kabbalistic terms.

(A disclaimer: With many such concepts there are varying ways of understanding them. I do not assume that the way I am presenting is universally accepted or even that it properly conveys the understanding of the authors who I am studying. This is my understanding.)

When we speak of כלים, vessels, it is a reference to a person's (or some other spiritual being's) capacity to engage with and assimilate a particular spiritual concept. Spirituality is spoken of in terms of light, אור, and specifically the light is spoken about in terms of אור פנימי, the Inner Light, and אור מקיף, the Light which Surrounds.

The light of Hashem's spirituality is infinite and can't possibly be fully assimilated by one of His Creations. The אור פנימי is the quantity of light that a person can take within himself. It is that which can fit within his vessel. That which he can comprehend. That which is beyond his ability to conceive of remains אור מקיף, hovering about on the outside. It is there, but unattainable, and in much greater quantity than that which has been taken in.