והיה ביום ההוא יתקע בשופר גדול ובאו האבדים בארץ אשור והנדחים בארץ מצרים ... (ישעיהו כז-יג)
Yeshaya HaNavi’s message of redemption parallels Hashem’s message to Moshe of Klal Yisroel’s redemption from Egypt. Interestingly, the Navi describes the returning people as "אבדים" and "נדחים" - two words that translate to mean lost and exiled. Was it so necessary for Yeshaya to use these two words that seem to have a redundant meaning?
R’ Shamshon Raphael Hirsch zt”l gives a beautiful explanation. Yeshaya HaNavi was referring to two separate segments of lost Jewish souls which would not normally be equated with one another, but now they are. The word "נדחים" usually refers to those who were forcibly removed and expelled from their land and heritage, while the word "אבדים" usually refers to those who have become lost. However, in this prophecy, "נדחים" refers to those who were “induced” into leaving the path of Torah and mitzvos, while "אבדים" makes reference to those members of Klal Yisroel whose ancestors chose to leave the fold and assimilate into the gentile world and culture. They have grown up not even knowing that they were Jewish and their existence and whereabouts have long faded from the awareness of their brethren.
Says R’ Hirsch, when Mashiach arrives and the heavenly shofar is sounded, these lost Jews (אבדים) who never even knew they were Jewish will be identified and brought back into the fold by those Jews who were tempted/forced away from their faith (נדחים) and together they will dedicate their lives to serving Hashem and doing His mitzvos.