What does grandpa say that grandpas are for?

From the text:

Rearing back and looking as important as Rowdy did when he had treed something. Grandpa said, "Sure I know something about those monkeys. That's what grandpas are for, isn't it? To know things for boys." (pg. 25)

"Taking the list. Grandpa smiled and said, "Well, that's what Grandpas are for, isn't it; to look out for boys?" (pg. 32)

"Do you have another plan. Grandpa?" I asked. "Sure, I have another plan," Grandpa said. "That's what grandpas are for, isn't it? Don't worry about catching those monkeys. Before you know it, we'll have every one of them in the sack." (pg. 74)