The most quoted is Piccarda's, in canto III: "and in his will is our peace: it is the sea toward which all that he creates and all that nature makes moves." It is the answer to Dante's question about whether she and the other souls do not desire a higher place, and it settles at once a doubt that will return in every heaven: to desire more would be to disagree with the will that makes them happy.
Two other passages dispute first place. The first is the last verse of the poem, the love that moves the sun and the other stars, which closes the whole Comedy on the same word with which the other canticles end: stars. The second is the beginning of Bernard's prayer to the Virgin, "Virgin Mother, daughter of your Son, humble and higher than any creature, fixed term of an eternal counsel," which gathers in a few lines the paradoxes of who Mary is.
Also much remembered are Cacciaguida's verse about exile, the bread of others that tastes of salt, and the definition of faith that Dante gives to Peter: substance of things hoped for and argument of things not seen. None of them alone sums up the canticle. Paradise is more a process than an image, and that is why the lines that summarize it say what a man can see, and what he can say of what he saw.