פירוש על כלים 19:2

החבל היוצא מן המטה – what remains from it [hangs over the bed] after he completed the plaiting.

A rope that hangs out from a bed:
If it is shorter than five handbreadths, it is clean,
If it is from five to ten handbreadths long, it is unclean.
From ten handbreadths and longer is clean;
For it is with [this rope] that paschal lambs were tied and beds were lowered down.
Today's mishnah deals with ropes that hang out from a bed after the main part of the rope was woven around the bed frame.
Section one: If the rope is less than five handbreadths long, it is not useful and it is not susceptible to impurity.
Sections two and four: If it is longer than five handbreadths, it is useful, but only the portion up to ten handbreadths is susceptible. Section four explains how they would use these ropes. The first use was to tie the paschal lamb to the bed in preparation for the lamb's slaughter on Pesah. On the original Pesah which was celebrated in Egypt it was required that one would set aside the lamb on the tenth of Nissan. This was not required on subsequent observations of the holiday, but evidently people did so in any case. My only explanation for why they would tie it to the bed is so that it wouldn't get mixed up with other non-paschal lambs, or with paschal lambs set aside by other people.
The other use was to lower their beds when taking them down from the roofs (where they sometimes slept) or for lowering them down into the mikveh.
Section four: Only the part that was between five and ten handbreadths was really needed. The rest of the rope was extraneous and therefore it is clean.

עד חמשה טפחים טהור – for it is not appropriate for the needs of the bed, and it is not considered a handle.

מחמשה ועד עשרה טמא – for it is appropriate to knot with it the Passover sacrifices. For they would regularly tie up the Passover sacrifices with a rope that is on the leg of the bed in order that it be ready for them. And it was appropriate also to let it down [over the side of the bed] , that is to say, to lower it from the attic to the roof. Alternatively, to lower it to the ritual bath to immerse it when it became defiled.

מעשרה ולחוץ טהור – for what there is on a rope more than ten [handbreadths] he does not use at all for the purposes of the bed.