Biblical Commentary on the Old Testament, by Carl Friedrich Keil and Franz Delitzsh, [1857-78], at sacred-texts.com
"The word which Jeremiah the prophet spake to Baruch the son of Neriah, when he wrote these words in a book at the mouth of Jeremiah, in the fourth year of Jehoiakim the son of Josiah king of Judah, saying, Jer 45:2. Thus saith Jahveh, the God of Israel, to thee, O Baruch: V. 3. Thou saidst, Woe to me now! for Jahveh hath added sorrow to my pain: I am weary with sighing, and no rest do I find. V. 4. Thus shalt thou say unto him, Thus saith Jahveh: Behold, what I have built I will destroy, and what I have planted I will pluck up, and that is the whole earth. V. 5. And thou seekest great things for thyself: seek them not: for, behold, I will bring evil on all flesh, saith Jahveh; but I will give thy life unto thee for booty in all places whither thou shalt go."
From the superscription in Jer 45:1, it appears that this word of God came to Baruch through Jeremiah the prophet, in the fourth year of the reign of Jehoiakim, when Baruch was writing out, or had written out, in a book-roll the prophecies that had been uttered by Jeremiah up till that time. It is not necessarily implied in the infin. בּכתבו that the word of God came during the transcription, while he was still engaged in writing: it may also mean, "when he was ready with the writing," had got done with it; and Hitzig is wrong when he rejects as "misleading" the view which Movers takes - "when he had written." The writing down of the addresses of Jeremiah in the year mentioned is related in Jer 36; thus the substance of this chapter and that of Jer 36 agree. "These words" can only be the addresses (words) of Jeremiah which Baruch was then writing down. From this, Hitzig, Graf, Ngelsbach, and others, infer that this small piece was the last in the copy of Jeremiah's prophecies originally prepared under Jehoiakim, - if not of the first one which was intended to be read in the temple, at least of the second copy which was made after the former one had been destroyed; and that it was only after the collection had been enlarged to the extent of the collection handed down to us, that this portion was affixed as an appendix to the end of the prophecies of Jeremiah which relate to his own country. But this inference is not a valid one. "These words" are the addresses of the prophet in general, which Baruch wrote down; and that only those which were uttered up to the fourth year of Jehoiakim are intended, is implied, not in the demonstrative "these," but in the date given afterwards, by which "these" is further specified. In Jer 45:1 it is merely stated that at that time the word of God, given below, came to Jeremiah, and through Him to Baruch, but not that Baruch wrote down this also on that occasion, and appended it to the roll of Jeremiah's prophecies which had been prepared at his dictation. It may have been written down much later, possibly not till the whole of Jeremiah's prophecies were collected and arranged in Egypt. Moreover, the position occupied by this chapter in the collection shows that this message of comfort to Baruch was added as an appendix to those predictions of Jeremiah which concern Judah and Israel.
The occasion for this message of comfort addressed to the prophet's attendant is pointed out in Jer 45:3, in the words which Baruch had uttered: "Woe to me! for Jahveh adds sorrow to my pain." Baruch felt "pain," i.e., pain of soul, at the moral corruption of the people, their impenitence and obduracy in sin and vice, just like the prophet himself, Jer 15:18. To this pain God adds sorrow, by threatening the judgment which shall fall on Judah for sin, and which was even then beginning to break over the land; cf. Jer 8:18. Baruch sighs over this till he is wearied, and finds no rest; cf. Lam 5:5. "I am weary with my sighing," is a reminiscence from Psa 6:7. This sorrow in addition to his pain was not caused in him for the first time by writing down the discourses of the prophet, but was rather thus freshened and increased. The answer of the Lord to this sighing is of a stern character, yet soothing for Baruch. The sentence of destruction has been determined on. What the Lord has built He will now destroy: it is not said why, since the reason was sufficiently known from the prophet's utterances. As to the expression in Jer 45:4, cf. Jer 1:10; Jer 31:28. The destruction regards the whole earth, היא ואת־כּל־הארץ, lit., "and as regards the whole earth, it is it," namely that I destroy. On the employment of את in introducing the subject, cf. Dan 9:13; Hag 2:5, and Ewald, 277 d. כּל־הארץ does not mean "the whole land," but "the whole earth:" this is indubitably evident from the parallel "upon all flesh," Jer 45:5, i.e., the whole of humanity, as in Jer 25:31. The sentence is passed on all the earth, in accordance with the announcement made in Jer 25:15.
But when the judgment extends over the whole of humanity, an individual man cannot ask for anything great. "To seek for great things," i.e., to ask for things which in general or under certain circumstances are unattainable (cf. Psa 131:1), is here used with reference to worldly prosperity. When the whole world is visited with judgment, an individual man must not make great demands, but be content with saving his life. This is promised to Baruch in Jer 45:5, to alleviate his pain and sorrow. "To give life to any one for booty," means to let him escape with his life; cf. Jer 21:9; Jer 38:2; Jer 39:18. In the words, "in all places whither thou shalt go," it is intimated that he will be obliged to avoid destruction by flight, but will thereby save his life.