Psalms 122:3 - Ellicott's Commentary On The Whole Bible

This verse is somewhat perplexing. It is explained to refer either to the rebuilding of the city and reuniting of the parts which had been disconnected in the destruction, or, which is far better (see Introduction), is taken as a rustic’s impression on first seeing a compact city after being accustomed to straggling villages. The astonishment of Virgil’s shepherd is aptly compared: “Urbem quam dicunt Romam, Melibæe putavi, Stultus ego, huic nostræ similem.” But a far more satisfactory meaning is suggested by the LXX. They (comp. Symmachus) take the word rendered compact as a noun, meaning union. The verse then may run: Jerusalem, the (one) built like a city, union is in it together, i.e., it is the rallying point of all the tribes. (See next verse.)