A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
jer 45:1JEREMIAH COMFORTS BARUCH. (Jer 45:1-5)
these words--his prophecies from the thirteenth year of Josiah to the fourth of Jehoiakim.
jer 45:3Thou didst say, &c.--Jeremiah does not spare his disciple, but unveils his fault, namely, fear for his life by reason of the suspicions which he incurred in the eyes of his countrymen (compare Jer 36:17), as if he was in sympathy with the Chaldeans (Jer 43:3), and instigator of Jeremiah; also ingratitude in speaking of his "grief," &c., whereas he ought to deem himself highly blessed in being employed by God to record Jeremiah's prophecies.
added--rescued from the peril of my first writing (Jer 36:26). I am again involved in a similar peril. He upbraids God as dealing harshly with him.
I fainted--rather, "I am weary."
no rest--no quiet resting-place.
jer 45:4that which I have built . . . planted I will pluck up-- (Isa 5:5). This whole nation (the Jews) which I founded and planted with such extraordinary care and favor, I will overthrow.
jer 45:5seekest thou great things for thyself--Thou art over-fastidious and self-seeking. When My own peculiar people, a "whole" nation (Jer 45:4), and the temple, are being given to ruin, dost thou expect to be exempt from all hardship? Baruch had raised his expectations too high in this world, and this made his distresses harder to be borne. The frowns of the world would not disquiet us if we did not so eagerly covet its smiles. What folly to seek great things for ourselves here, where everything is little, and nothing certain!
all flesh--the whole Jewish nation and even foreign peoples (Jer 25:26).
but thy life . . . for a prey--Esteem it enough at such a general crisis that thy life shall be granted thee. Be content with this boon of life which I will rescue from imminent death, even as when all things are given up to plunder, if one escape with aught, he has a something saved as his "prey" (Jer 21:9). It is striking how Jeremiah, who once used such complaining language himself, is enabled now to minister the counsel requisite for Baruch when falling into the same sin (Jer 12:1-5; Jer 15:10-18). This is part of God's design in suffering His servants to be tempted, that their temptations may adapt them for ministering to their fellow servants when tempted.
He begins with Egypt, being the country to which he had been removed. The forty-sixth chapter contains two prophecies concerning it: the discomfiture of Pharaoh-necho at Carchemish by Nebuchadnezzar, and the long subsequent conquest of Egypt by the same king; also the preservation of the Jews (Jer 46:27-28).