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 42:2THE JEWS AND JOHANAN INQUIRE OF GOD, THROUGH JEREMIAH, AS TO GOING TO EGYPT, PROMISING OBEDIENCE TO HIS WILL. THEIR SAFETY ON CONDITION OF STAYING IN JUDEA, AND THEIR DESTRUCTION IN THE EVENT OF GOING TO EGYPT, ARE FORETOLD. THEM HYPOCRISY IN ASKING FOR COUNSEL WHICH THEY MEANT NOT TO FOLLOW, IF CONTRARY TO THEIR OWN DETERMINATION, IS REPROVED. (Jer. 42:1-22)
Jeremiah--He probably was one of the number carried off from Mizpah, and dwelt with Johanan (Jer 41:16). Hence the expression is, "came near" (Jer 42:1), not "sent."
Let . . . supplication be accepted--literally, "fall" (see on Jer 36:7; Jer 37:20).
pray for us-- (Gen 20:7; Isa 37:4; Jam 5:16).
thy God-- (Jer 42:5). The Jews use this form to express their belief in the peculiar relation in which Jeremiah stood to God as His accredited prophet. Jeremiah in his reply reminds them that God is their God ("your God") as well as his as being the covenant people (Jer 42:4). They in turn acknowledge this in Jer 42:6, "the Lord our God."
few of many--as had been foretold (Lev 26:22).
jer 42:3They consulted God, like many, not so much to know what was right, as wishing Him to authorize what they had already determined on, whether agreeable to His will or not. So Ahab in consulting Micaiah (Kg1 22:13). Compare Jeremiah's answer (Jer 42:4) with Micaiah's (Kg1 22:14).
jer 42:4I have heard--that is, I accede to your request.
your God--Being His by adoption, ye are not your own, and are bound to whatever He wills (Exo 19:5-6; Co1 6:19-20).
answer you--that is, through me.
keep nothing back-- (Sa1 3:18; Act 20:20).
jer 42:5Lord be a true . . . witness-- (Gen 31:50; Psa 89:37; Rev 1:5; Rev 3:14; Rev 19:11).
jer 42:6evil--not moral evil, which God cannot command (Jam 1:13), but what may be disagreeable and hard to us. Piety obeys God, without questioning, at all costs. See the instance defective in this, that it obeyed only so far as was agreeable to itself (Sa1 15:3, Sa1 15:9, Sa1 15:13-15, Sa1 15:20-23).
jer 42:7ten days--Jeremiah did not speak of himself, but waited God's time and revelation, showing the reality of his inspiration. Man left to himself would have given an immediate response to the people, who were impatient of delay. The delay was designed to test the sincerity of their professed willingness to obey, and that they should have full time to deliberate (Deu 8:2). True obedience bows to God's time, as well as His way and will.
jer 42:10If ye . . . abide--namely, under the Babylonian authority, to which God hath appointed that all should be subject (Dan 2:37-38). To resist was to resist God.
build . . . plant--metaphor for, I will firmly establish you (Jer 24:6).
I repent . . . of the evil-- (Jer 18:8; Deu 32:36). I am satisfied with the punishment I have inflicted on you, if only you add not a new offense [GROTIUS]. God is said to "repent," when He alters His outward ways of dealing.
jer 42:12show mercies--rather, I will excite (in him) feelings of mercy towards you [CALVIN].
cause you to return--permit you to return to the peaceable enjoyment of the possessions from which you are wishing to withdraw through fear of the Chaldeans. By departing in disobedience they should incur the very evils they wished thereby to escape; and by staying they should gain the blessings which they feared to lose by doing so.
jer 42:13if ye say, &c.--avowed rebellion against God, who had often (Deu 17:16), as now, forbidden their going to Egypt, lest they should be entangled in its idolatry.
jer 42:14where we shall see no war--Here they betray their impiety in not believing God's promise (Jer 42:10-11), as if He were a liar (Jo1 5:10).
jer 42:15wholly set your faces--firmly resolve (Luk 9:51) in spite of all warnings (Jer 44:12).
jer 42:16sword, which ye feared, shall overtake you--The very evils we think to escape by sin, we bring on ourselves thereby. What our hearts are most set on often proves fatal to us. Those who think to escape troubles by changing their place will find them wherever they go (Eze 11:8). The "sword" here is that of Nebuchadnezzar, who fulfilled the prediction in his expedition to Africa (according to MEGASTHENES, a heathen writer),300 B.C.
jer 42:17all the men--excepting the "small number" mentioned (Jer 44:14, Jer 44:28); namely, those who were forced into Egypt against their will, Jeremiah, Baruch, &c., and those who took Jeremiah's advice and fled from Egypt before the arrival of the Chaldeans.
jer 42:18As mine anger, &c.--As ye have already, to your sorrow, found Me true to My word, so shall ye again (Jer 7:20; Jer 18:16).
shall see this place no more--Ye shall not return to Judea, as those shall who have been removed to Babylon.
jer 42:19I have admonished--literally, "testified," that is, solemnly admonished, having yourselves as My witnesses; so that if ye perish, ye yourselves will have to confess that it was through your own fault, not through ignorance, ye perished.
jer 42:20dissembled in your hearts--rather, "ye have used deceit against your (own) souls." It is not God, but yourselves, whom ye deceive, to your own ruin, by your own dissimulation (Gal 6:7) [CALVIN]. But the words following accord best with English Version, ye have dissembled in your hearts (see on Jer 42:3) towards me, when ye sent me to consult God for you.
jer 42:21declared it--namely, the divine will.
I . . . but ye--antithesis. I have done my part; but ye do not yours. It is no fault of mine that ye act not rightly.
jer 42:22sojourn--for a time, until they could return to their country. They expected, therefore, to be restored, in spite of God's prediction to the contrary.