A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 122:1This Psalm might well express the sacred joy of the pilgrims on entering the holy city, where praise, as the religious as well as civil metropolis, is celebrated, and for whose prosperity, as representing the Church, prayer is offered. (Psa 122:1-9)
Our feet shall stand--literally, "are standing."
psa 122:2gates--(Compare Psa 9:14; Psa 87:2).
psa 122:3compact together--all parts united, as in David's time.
psa 122:4testimony--If "unto" is supplied, this may denote the ark (Exo 25:10-21); otherwise the act of going is denoted, called a testimony in allusion to the requisition (Deu 16:16), with which it was a compliance.
psa 122:5there are set thrones--or, "do sit, thrones," used for the occupants, David's sons (Sa2 8:18).
psa 122:6Let peace--including prosperity, everywhere prevail.
psa 122:8In the welfare of the city, as its civil, and especially the religious relations, was involved that of Israel.
now--as in Psa 115:2.
psa 122:9Let me say--house of . . . God--in wider sense, the Church, whose welfare would be promoted by the good of Jerusalem.