To swell a progress
In Hamlet, Rosencrantz and Guildenstern aren’t tremendously significant figures in their own right. They’re important in the plot: they are Hamlet’s friends, and because he is thought to like them and heed their advice they are recruited to spy on him. Prufrock thinks his destiny is similar. He may play a minor role in a larger story, or swell the numbers of a royal court, but he’s basically not a very big deal. He’s like an extra in a film or a hanger-on in an entourage.
To help improve the meaning of these lyrics, visit "The Love Song Of J. Alfred Prufrock" by T.S. Eliot and leave a comment on the lyrics box