This year Jonathan Will, age 15, is getting the greatest gift that can be given: a friend. The fact that this friend, a large dog, does not need to be wrapped is but one of its merits.

Her merits. Angel is a blond Labrador. About her, as about all members of that dignified species, there clings, like banker's worsted, the aura of knowing what is best but being too well-bred to insist on it. So she will improve the tone of the household, as she has done of Christmas.

''We shall soon be having Christmas at our throats,'' says a P. G. Wodehouse character who should be ashamed of himself. The routs and revels that erupt in connection with Christmas do take their toll on body and soul. Once you have had your fill of eggnog, which is easy to do, and once you have dusted from your shirt front the sugar from the pfeffernusse cookies, and once you have chewed through those gummy bits that make eating fruitcake such hard exercise, when you have done those things you have pretty well drained Christmas of most of what it has to offer in the way of physical pleasures.

Furthermore, Christmas Eve invariably is a Walpurgisnacht of trips to drugstores for batteries that were not included in the box containing (you will discover on Christmas Day) 42,389 of the 42,390 parts in the do-it-yourself mainframe computer. On the box are printed those three terrible words: ''Some Assembly Required.''

Dogs come assembled and need no batteries. Blessed Angel is 6 and has graduated from finishing school and is ready to do what dogs do. A cynic once said that to his dog, every man is Napoleon, hence the popularity of dogs. Actually, no sensible person wants to feel like a Corsican brigand, so for ''Napoleon'' substitute, say, ''Alan Greenspan.'' Dogs make us feel lofty but not so forbiddingly grand as to be unapproachable.

A philosophic dog like a Labrador will, if given half a chance, give to us the closest we are apt to come to unconditional love. Pedants may take issue with the ascription of love to an animal. But however we categorize what dogs do for us, it is what it is, and it comes down to this: our dogs are always glad to see us. They want to step high, wide and plentiful with us, and then doze in the sun in close proximity to us.

These days Jonathan is a boy of the great indoors, having discovered Bon Jovi (a rock group) and the teen-age pleasure of sovereignty in one's own room. Angel -- who, by the way, is approximately the color of rich Devon cream -- presumably will put up with a lot of Bon Jovi. But she also will insist on brisk walks, which will do both of them a world of good.

Jonathan is handicapped (Down's syndrome) and sometimes has trouble making his abundant thoughts and feelings understood by strangers. So at times, with poignant urgency, he has turned for companionship to a neighbor's dog, another blond Lab, named Skylab.

There is a large lesson here about the handicapped. Jon is just like everyone else, only a bit more so, in the following sense.

A shadow of loneliness is inseparable from the fact of individual existence. This shadow is perhaps somewhat darker for people like Jon because their ability to articulate -- the ability by which we all cope with the apartness that defines ourcondition -- is, even more than for most of us, not commensurate to their abilities to think and feel.

So Jon has found, as all dog lovers do, consolation in the company of a four-legged friend. If Skylab could speak -- and, come to think about it, he does, with eloquent body language from tongue to tail -- he would testify to the fact that Jon's handicap is no impediment to the flow of friendship.

In fact, watching the reciprocated pleasure between Jon and Skylab, I have come to a conclusion suited to this season. It is that some small mitigation of the harshness of life's lottery, some gently compensating thumb on the scale of justice, has given Jon an enlarged talent for friendship, with people and with their best friends.

So this year Jon gets Angel. Or Angel gets Jon, which is much the same thing. The unencumbered mutuality, the free flowing of giving between a dog and a boy, is a lesson in life's goodness, and the lesson is part of the greatest gift.