Charles Ellicott Commentary Jeremiah 50:20

"In those days, and in that time, saith Jehovah, the iniquity of Israel shall be sought for, and there shall be none; and the sins of Judah, and they shall not be found: for I will pardon them whom I leave as a remnant." — Jeremiah 50:20 (ASV)

In those days, and in that time ... —The formula is that which in prophetic language points to the far-off times of the Christ. Their restoration to their earthly homes was only a small thing. What was to the prophet the great blessing of the future was that it would bring with it the New Covenant of Jeremiah 31:31, pardon and peace, iniquity and sin remembered no more.

I will pardon them whom I reserve. —The latter verb contains the root of the “remnant” which is so prominent in Isaiah (Isaiah 1:9; Isaiah 7:3), and expresses the same thought. “The remnant,” the reserved ones, will be pardoned.