John Gill Commentary Lamentations 3:1

"I am the man that hath seen affliction by the rod of his wrath." — Lamentations 3:1 (ASV)

I [am] the man [that] has seen affliction
Had much experience of it, especially ever since he had been a prophet; being reproached and ill used by his own people, and suffering with them in their calamities; particularly, as Jarchi observes, his affliction was greater than the other prophets, who indeed prophesied of the destruction of the city and temple, but did not see it; whereas he lived to see it: he was not indeed the only man that endured affliction, but he was remarkable for his afflictions; he had a large share of them, and was herein a type of Christ, who was a man of sorrows, and acquainted with griefs:

by the rod of his wrath ;
that is, by the rod of the wrath of God, for he is understood; it is a relative without an antecedent, as in (Song of Solomon 1:1) ; unless the words are to be considered in connection (Lamentations 2:22) . The Targum is, ``by the rod of him that chastiseth in his anger;'' so Jarchi; but God's chastisements of his own people are in love, though thought sometimes by them to be in wrath and hot displeasure; so the prophet imagined, but it was not so; perhaps some regard may be had to the instrument of Jerusalem's destruction, the king of Babylon, called the rod of the Lord's anger, (Isaiah 10:5) ; all this was true of Christ, as the surety of his people, and as sustaining their persons, and standing in their room.