Passage
Behold thou their sitting down, and their rising up; I am their song.
Behold thou their sitting down, and their rising up; I am their song.
Lamentations 3:61 Thou hast heard their reproach, O Jehovah, and all their devices against me,
Lamentations 3:62 The lips of those that rose up against me, and their device against me all the day.
Lamentations 3:63 Behold thou their sitting down, and their rising up; I am their song.
Lamentations 3:64 Thou wilt render unto them a recompense, O Jehovah, according to the work of their hands.
Lamentations 3:65 Thou wilt give them hardness of heart, thy curse unto them.
The verse centers on "behold", "thou", "sitting", "down", "rising", and "song". It is saying that the verse draws attention to "behold" and "thou", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 62's "The lips of those that rose up..." into verse 64's "Thou wilt render unto them a recompense...", so "behold" and "thou" belong inside that flow. In Lamentations context, the local focus is covenant, worship, and faithfulness.
A plain takeaway is to answer the verse's own emphasis on "behold" and "thou" with trust shaped by these words, not by a vague optimism outside the passage.