Quote 1
"You see the mounds? I come here and prayed, nows and thens, when I thought maybe a Sunday would be about doo. It weren't quite a chapel, but it seemed more solemn like; and then, says you, Ben Gunn was short-handed--no chapling, nor so much as a Bible and a flag, you says."
So he kept talking as I ran, neither expecting nor receiving any answer. (15.54-5)
As Ben Gunn and Jim travel across the island, Gunn keeps narrating as though he is alone and doesn't expect a response from his audience. He is clearly used to talking to himself, which reminds us that he has been alone for three years. Stevenson is amazingly skilled at using language to suggest character. Here, we definitely get the sense that Ben Gunn has gotten a little weird during his years of solitude.
Quote 2
"Ah, well," said [Ben Gunn], "but I had--remarkable pious. And I was a civil, pious boy, and could rattle off my catechism that fast, as you couldn't tell one word from another. And here's what it come to, Jim, and it begun with chuck-farthen on the blessed grave-stones! That's what it begun with, but it went further'n that; and so my mother told me, and predicked the whole, she did, the pious woman! But it were Providence that put me here. I've thought it all out in this here lonely island, and I'm back on piety. You don't catch me tasting rum so much, but just a thimbleful for luck, of course, the first chance I have. I'm bound I'll be good, and I see the way to. And, Jim"--looking all round him and lowering his voice to a whisper--"I'm rich." (15.22)
Ben Gunn has spent three years on Treasure Island, and all this time alone has made him decide to go back to God (he's "back on piety"). But we can already see signs that he's just waiting for the chance to go back to his old ways. Even though he swears that "you don't catch me tasting rum so much," he'd take "a thimbleful for luck [...] the first chance [he has]." And indeed, the first chance Gunn has to drink a thimbleful of rum, he doesn't stop there: he goes on a nineteen-day bender that leaves him penniless. We find the foreshadowing of this future self-indulgence right here in his speech on the island.