If thou hast run with the {f} footmen, and they have wearied thee, then how canst thou contend with horses? and if in the land of peace, in which thou didst trust, they wearied thee, then how wilt thou do in the swelling of Jordan?

(f) Some think that God reproves Jeremiah, in that he would reason with him, saying that if he was not able to march with men, then he was far unable to dispute with God. Others, by the footmen mean them of Anathoth: and by the horsemen, them of Jerusalem who would trouble the prophet worse than his own countrymen did.

Wesley's Notes

12:5 If - If thou art not able to encounter lesser dangers, how wilt thou be able to overcome greater? I have greater dangers for thee to encounter than those at Anathoth; if thou art so disturbed with them, how wilt thou be able to grapple with those at Jerusalem. Jordan - Anathoth seems to be understood by the land of thy peace, that is, the land of thy friends wherein thou hadst a confidence: if thy enemies there tire thee, what wilt thou do in the swellings of Jordan? In a place in which thou art like to meet with greater troubles, like the swelling of Jordan (which in harvest used to overflow its banks).

Scofield Reference Notes

Margin swelling of Jordan

i.e. under such a test as in Jer 49:19 50:44 Josh 3:15 1Chr 12:15

Jamieson-Fausset-Brown Bible Commentary

5. Jehovah's reply to Jeremiah's complaint.

horses-that is, horsemen: the argument a fortiori. A proverbial phrase. The injuries done thee by the men of Anathoth ("the footmen") are small compared with those which the men of Jerusalem ("the horsemen") are about to inflict on thee. If the former weary thee out, how wilt thou contend with the king, the court, and the priests at Jerusalem?

wherein thou trustedst, they wearied thee-English Version thus fills up the sentence with the italicized words, to answer to the parallel clause in the first sentence of the verse. The parallelism is, however, sufficiently retained with a less ellipsis: "If (it is only) in a land of peace thou art confident" [Maurer].

swelling of Jordan-In harvest-time and earlier (April and May) it overflows its banks (Jos 3:15), and fills the valley called the Ghor. Or, "the pride of Jordan," namely, its wooded banks abounding in lions and other wild beasts (Jer 49:19; 50:44; Zec 11:3; compare 2Ki 6:2). Maundrell says that between the Sea of Tiberias and Lake Merom the banks are so wooded that the traveller cannot see the river at all without first passing through the woods. If in the champaign country (alone) thou art secure, how wilt thou do when thou fallest into the wooded haunts of wild beasts?

Matthew Henry's Concise Commentary

12:1-6 When we are most in the dark concerning God's dispensations, we must keep up right thoughts of God, believing that he never did the least wrong to any of his creatures. When we find it hard to understand any of his dealings with us, or others, we must look to general truths as our first principles, and abide by them: the Lord is righteous. The God with whom we have to do, knows how our hearts are toward him. He knows both the guile of the hypocrite and the sincerity of the upright. Divine judgments would pull the wicked out of their pasture as sheep for the slaughter. This fruitful land was turned into barrenness for the wickedness of those that dwelt therein. The Lord reproved the prophet. The opposition of the men of Anathoth was not so formidable as what he must expect from the rulers of Judah. Our grief that there should be so much evil is often mixed with peevishness on account of the trials it occasions us. And in this our favoured day, and under our trifling difficulties, let us consider how we should behave, if called to sufferings like those of saints in former ages.