What does the author do to keep the chapters from being too dark and tragic?

Dickens throws a bit of levity into chapter 55,

Next Monday arrives, and Pip goes to Wemmick’s castle. Wemmick is around, but the Aged is nowhere in sight. Wemmick grabs his fishing rod and the two set out on their hike.

They walk by a church, and Wemmick says, "Halloa! Here’s a church!" (3.55.48) and the two go inside.

There happen to be a pair of gloves inside the church, and Wemmick suggest they put them on.

Pip does so, but he has no clue as to what in the hey is going on.

Miss Skiffins appears on the arm of the Aged, and Wemmick says, "Here’s Miss Skiffins! Let’s have a wedding" (3.55.54). In this way, Pip becomes Wemmick’s best man.

The four of them go to the local inn after the wedding ceremony and have a delicious wedding breakfast.