The speaker imagines a future return to the hill where a couple married, and predicts that they will laugh there. What they will laugh at is the interesting part: themselves, the world, and the "peak" they think they have reached. The pun on "peak" works two ways. It is a literal hilltop, and it is also the high point of life, the sense of having arrived somewhere important. Looking back, the speaker expects that grand feeling to seem a little funny.
Yet the tone is gentle, not mocking. The final lines promise that the laughter "will do no hurt / to the quiet," as if the hill's stillness is something precious that their amusement won't disturb. The mood is warm, humble and calm. The speaker seems to value a love that can laugh at its own solemnity, and that sits comfortably inside a larger silence. Short lines and spare wording add to the hushed, unhurried feel.