Keilim, Chapter 25, Mishnah 9. Throughout this chapter the Mishnah has been distinguishing between the different surfaces of a keli: its inside (toch), its outside (achorayim), and the small area where a person grips it with his fingers (beit hatzevia). Those distinctions produce a number of leniencies, since tumah that reaches one part does not automatically spread to the others. Our mishnah now teaches that all of those leniencies fall away when the utensil is used for kodesh: a keli of holiness is treated with greater severity than every keli discussed until now.
No division between inside and outside
"Kelei hakodesh ein lahem achorayim vetoch": utensils used for holy purposes have no separate law of outside and inside. With an ordinary keli, tamei liquid that touches only the outer surface renders the outside tamei while the inside remains pure. For a keli of kodesh there is no such split. Whether the tamei liquid comes into contact with the exterior or with the interior, the entire utensil becomes tamei.
No separate status for the grip
"Ve'ein lahem beit hatzevia": the finger-hold enjoys no independent status either. In an ordinary keli we reckon with three zones that can each stand on its own halachically: the interior, the outer wall, and the narrow spot grasped between the fingers. Tumah that lands on the grip need not travel to the exterior, and tumah on the exterior need not reach the grip. For a keli that serves kodesh the Mishnah decides otherwise: grip and body count as a single unit, so tumah touching any point on it renders the vessel tamei in its entirety.
Immersing one keli inside another
The Mishnah continues, "ein matbilin kelim betoch kelim" when the immersion is "lakodesh": vessels may not be dipped one within another. Suppose a person wants to purify two utensils in a single immersion and thinks to set the smaller one inside the larger. Where kodesh is involved this is not permitted, since the inner utensil is liable to lie tight against the outer one, sealing off the spot where they meet so that the water of the mikveh never washes those surfaces. Each utensil must go into the water by itself, another severity that belongs to kelei hakodesh alone.
How a keli acquires and loses susceptibility to tumah
"Kol hakelim yordin lidei tum'atan bemachshavah": a vessel becomes capable of contracting tumah by means of intention. A person may own an item that in its present condition stands outside the laws of tumah altogether; the moment he resolves in his heart to press it into service as a utensil, it has become a keli, and whatever qualifies as a keli can contract tumah. Nothing needs to be done to the object physically for this to take effect.
"Ve'einan olim midei tum'atan ella beshinuy ma'aseh": release from that susceptibility comes about only when a deed effects a change in the object itself. Should the vessel already be tamei, or already stand within the category of things able to become tamei, it retains that standing until it is physically altered.
The principle behind the rule
"Shehama'aseh mevatel miyad hama'aseh umiyad hamachshavah": the halachah rests on the fact that a deed is able to nullify whatever preceded it, be that an earlier deed or an earlier intention. "Umachshavah einah mevatelet": intention carries no such force, neither against a deed that came before it ("lo miyad ma'aseh") nor against an earlier intention ("velo miyad machshavah"). Practically, then, a vessel that entered the realm of tumah through nothing more than a person's thought cannot be taken out of it by a second thought. Only a real deed has the strength to shift the standing of a keli.