וּמִדַּלַּ֣ת הָאָ֔רֶץ הִשְׁאִ֖יר רַב־טַבָּחִ֑ים לְכֹֽרְמִ֖ים וּלְיֹגְבִֽים׃
But the captain of the guard left of the poorest of the land to be vinedressers and husbandmen.
Radak
Say — They said "on the fifth and the severth" even though there are four fast days. It mentions the fifth because upon it was the destruction, and the seventh because in it Gedaliah was killed, and it was a second destruction, because already the poorest of the land remained and were not destroyed, since the poorest of the land were kept by Nebuzadaran to be vine dressers and ditch diggers (II Kings 25:12), but Gedaliah was killed on the first day of the seventh month, and since it was a holiday they declared a fast the day after.