Jamieson, Fausset and Brown on Isaiah 60:18

18. (Is 2:4). Not only shall thy walls keep thee safe from foes, but "Salvation" shall serve as thy walls, converting thy foes into friends, and so ensuring thee perfect safety (Is 26:1, 2).

gates--once the scene of "destruction" when victorious foes burst through them (Ne 1:3); henceforth to be not only the scene of praises, but "Praise" itself; the "gates," as the place of public concourse, were the scene of thanksgivings (2Ch 31:2; Psa 9:14; 24:7; 100:4). "Judah," the favored tribe, means "praise."