1. Toast pine nuts in a small, dry skillet over medium-high heat, shaking skillet constantly, until lightly browned and fragrant, 2 to 3 minutes. Transfer to a bowl to cool.
2. Cut stems from chard; trim ends. Cut stems into 1/4-inch slices. Slice leaves crosswise into 1/2-inch-wide strips.
3. Melt butter in a pot over medium-high heat. Cook chard stems, stirring, until softened, 2 to 4 minutes. Stir in raisins and 1/2 cup water. Cover, reduce heat to low and simmer for 3 minutes or until raisins are soft. Add leaves in batches, pushing down cooked greens to make room for new ones as they wilt. Cook, stirring often, until chard is tender but still slightly crisp, 3 to 5 minutes.
4. Just before serving, drain off any excess liquid and toss chard mixture with pine nuts and vinegar. Season with salt and pepper. Serve hot.