Our speaker in "My Heart Leaps Up When I Behold" seems like a pretty tranquil, but resolute, guy. He loves nature, always has, and always will. We know that he's male, and an adult, as he refers to being a man "now."
Even though he's a man, our speaker seems pretty connected to his childhood, even saying that "The Child is father of the Man" (7). Think about that for a minute, though. Would this sort of sentiment fly today? Isn't "grow up," something you hear a lot. This speaker is not your typical "man," who has left his childhood far behind and "matured" into adulthood. No, he's still deeply connected to the values of his youth.
Don't mistake this for some early version of Big, though. It's not like the guy has never developed. In fact, he's very aware of the reasons for his connection to his childhood: namely, to stay connected to the awe and wonder that the natural world can provide.
Today, we tend to poo-poo this kind of attitude, or else see it as some sort of joke. But our speaker is not joking here. He's seriously spiritual about being in nature. It's a kind of religious experience for him, and one that he traces back to his earliest years. For him, childhood isn't something to outgrow like a pair of underoos. It's a source of vitality and peace. Kind of makes you wish you were more of a kid, doesn't it?