Is treatment of the body after death of any concern to the departed soul? Does a ritual washing accomplish anything? Is the interval between death, and subsequent burial or cremation of any importance?

These things are cultural in origin and not of any material value to the departed soul. So any benefits are to the loved ones still in the living who may draw comfort from a ritual gesture of love which is the purpose of the washing. It is a parting gift to put that individual in the best possible shape to meet their maker, so to speak, and that is simply a gesture of love being bestowed. That does have benefits, even to the departed soul, because all thoughts and gestures of love will register with that spirit, and be known and noticed, and will bring the energy of consciousness from the Light to visit whoever is making that gesture. It will not be perceived, in most instances, that the spirit is present, but that is not the point. It nonetheless is the action of love and is a positive thing. It does uplift both parties as always is the case with a gesture of love that is acted upon. No ritual that is based in a loving thought or loving kindness is wasted because it always uplifts the person acting out the impulse, and that is a blessing for them to have an upliftment through a greater flow of love coming into them and being transmitted to its target. That is the major benefit of such rituals—it raises up the living and gives them nourishment and a bit of extra love at a very difficult time in their lives and that is always worthwhile. The issue of having cording to the body so that the body cannot be disturbed until the soul has truly made its way to the Light, is a metaphysical misinterpretation intuitively, of the problem of the lost soul, knowing that the energy of someone leaving the body can remain as an earthbound spirit as though it is still tethered to the body, and this is not strictly the case. There may be curiosity and there may be situations where the departing spirit will stay close to the body and wait to see what happens, but that is not because it is held there through the cording. They are free to journey about. Whether they do or not depends on their conscious will and perception of its possibility. Some newly departed spirits remain quite stuck and cannot move about at all. It is because they have lost their perception of where they are and how to navigate. This too is not the result of cording to anything holding them in place, it is an emotional and spiritual state of disconnection from awareness and has a different solution. So there is no particular need to honor the body, or to shield, or protect it from anything in particular. The rituals of funeral services and burial are, for practical reasons, to deal with the problem of decay and to honor the dead as a loving gesture, both of which have practical value for the living.