This passage of "An Essay on Criticism" is packed with alliteration. In fact, the "Essay" as a whole, and Pope's work in general, uses this device frequently. Pope was known for his witty, epigrammatic style, and alliteration helps make his observations all the more crisp and memorable.
It's no accident, for example, that the famous and often-quoted first line of this passage—"A little learning is a dangerous thing"—features an alliterative phrase. That line then pairs with the second half of its rhyming couplet, which starts with alliteration:
Drink deep, or taste not the Pierian spring:
Notice, too, how the /d/ sounds here echo the one in "dangerous" (line 1), and how the /dr/ sound echoes more faintly in the following lines ("draughts," "drinking"). All in all, these sonic repetitions make for a tightly woven, highly memorable four lines.
Once readers start noticing the alliteration in this passage, they'll realize how deliberate it is. Phrases like "strange surprise," "scenes of endless science," and "labours of the lengthened way" are clearly meant to please the ear and trip off the tongue.
In general, Pope was highly conscious of sound effects in his poetry—the "Essay on Criticism" features his famous, and alliterative, claim that "The sound must seem an echo to the sense"—and he specialized in writing lines that stick in the mind. (He's been called the most quotable author in the English language after Shakespeare!) Zingy, alliterative language is a big part of what makes his style so catchy.