(Isa. 48:20; Jer. 25:11; 29:10)
The Lord promised ancient Israel that after seventy years of Babylonian captivity, Israel would be blessed to return to the land of her inheritance (Jer. 25:11; 29:10). A second meaning is to leave the carnal world for the spiritual.
(Donald W. Parry, Jay A. Parry, and Tina M. Peterson, Understanding Isaiah [Salt Lake City: Deseret Book Co., 1998], 421.)
Verse 20 also seems to hold a double meaning. Israel was commanded to go forth from Babylon in a literal sense, and this they did when they returned to Jerusalem in 538 b.c. Through Cyrus, the Lord redeemed his people and brought them out of Babylon after they had endured fifty years of captivity. But Israel was also commanded to go forth or flee from Babylon in a spiritual sense. In a revelation given to the Prophet Joseph Smith in 1831, when the Church was still young, the Lord issued a similar command, adding a few words of clarification: “Go ye out from among the nations, even from Babylon, from the midst of wickedness, which is spiritual Babylon” (D&C 133:14). Thus ancient Israel was to go forth from the literal place called Babylon as well as to flee from the wickedness and spiritual corruption that existed in their world—just as modern Israel has been commanded to do.
(Andrew C. Skinner, Isaiah in the Book of Mormon, ed. Donald W. Parry and John W. Welch [Provo, Utah: Foundation for Ancient Research and Mormon Studies, 1998], 103.)