Jamieson, Fausset and Brown on Lamentations 1:7

7. remembered--rather, "remembers," now, in her afflicted state. In the days of her prosperity she did not appreciate, as she ought, the favors of God to her. Now, awakening out of her past lethargy, she feels from what high privileges she has fallen.

when her people fell, &c.--that is, after which days of prosperity "her people fell."

mock at her sabbaths--The heathen used to mock at the Jews' Sabbath, as showing their idleness, and term them Sabbatarians [Martial, 4.4]. Now, said they ironically, ye may keep a continuous Sabbath. So God appointed the length of the captivity (seventy years) to be exactly that of the sum of the Sabbaths in the four hundred ninety years in which the land was denied its Sabbaths (Le 26:33-35). Maurer translates it "ruin." But English Version better expresses the point of their "mocking," namely, their involuntary "Sabbaths," that is, the cessation of all national movements. A fourth line is added in this stanza, whereas in all the others there are but three. So in La 2:19.

Cheth.