Can you please explain the canto VII, XX and LXXVIII of the poem In Memoriam?

In Canto VII Tennyson is reminded of his late friend, Hallam, by visiting the place (the "dark house") where Hallam once lived. At night, the memory keeps Tennyson awake, and so he finds himself wandering around the house. In the early hours, he opens the door, half-expecting to find his friend there, but of course he isn't. The day comes to life, the hustle and bustle of the streets heard through the falling drizzle.
This canto poignantly expresses Tennyson's enormous sense of loss over the death of Hallam. Even though his friend is no longer with him, he still feels his presence.
In Canto XX Tennyson uses servants as a metaphor to describe what he calls his "lesser griefs," that is, the ordinary little everyday miseries that affect most of us in life. These "servants" will never have another "master" to serve like Tennyson's dear, departed friend. In his absence they can do no more than acknowledge how good and kind he was.
When we reach Canto LXXVIII Tennyson and his family are once more celebrating Christmas without Hallam. On the surface, everything seems fine, with everyone enjoying the festive season. Appearances are deceptive, however. For the joy of the Christmas holiday merely serves to remind Tennyson of happier times, of past Christmases spent with his special friend. He indulges in festive games with his family and friends, just as he once did with Hallam, but it is not quite the same. And although Tennyson doesn't cry, he still feels so terribly sad inside.