Jeremiah 31:18

We have here, I. Ephraim's repentance, and return to God. Not only Judah, but Ephraim the ten tribes, shall be restored, and therefore shall thus be prepared and qualified for it, Hos 14:8. Ephraim shall say, What have I do to any more with idols? Ephraim the people, is here spoken of as a single person to denote their unanimity; they shall be as one man in their repentance and shall glorify God in it with one mind and one mouth, one and all. it is likewise thus expressed that it might be the better accommodated to particular penitents, for whose direction and encouragement this passage is intended. Ephraim is here brought in weeping for sin, perhaps because Ephraim, the person from whom that tribe had its denomination, was a man of a tender spirit, mourned for his children many days (Ch1 7:21, Ch1 7:22), and sorrow for sin is compared to that for an only son. This penitent is here brought in, 1. Bemoaning himself and the miseries of his present case. True penitents do thus bemoan themselves. 2. Accusing himself, laying a load upon himself as a sinner, a great sinner.

— Matthew Henry's Concise Commentary (public domain)

Ephraim--representing the ten tribes. bemoaning himself--The spirit of penitent supplication shall at last be poured on Israel as the necessary forerunner of their restoration (Zac 12:10-14). Thou hast chastised me, and I was chastised--In the first clause the chastisement itself is meant; in the second the beneficial effect of it in teaching the penitent true wisdom. bullock unaccustomed to . . . yoke--A similar image occurs in Deu 32:15. Compare "stiff-necked," Act 7:51; Exo 32:9, an image from refractory oxen. Before my chastisement I needed the severe correction I received, as much as an untamed bullock needs the goad. Compare Act 9:5, where the same figure is used of Saul while unconverted. Israel has had a longer chastisement than Judah, not having been restored even at the Jews' return from Babylon. Hereafter, at its restoration, it shall confess the sore discipline was all needed to "accustom" it to God's "easy yoke" (Mat 11:29-30). turn thou me--by Thy converting Spirit (Lam 5:21). But why does Ephraim pray for conversion, seeing that he is already converted? Because we are converted by progressive steps, and need the same power of God to carry forward, as to originate, our conversion (Joh 6:44, Joh 6:65; compare with Isa 27:3; Pe1 1:5; Phi 1:6).

— Jamieson-Fausset-Brown Commentary (public domain)