Joel 2:12

turn ye even to me come back from your self-chosen course of sin, return to Me. On the idea of turning(or returning) to God in the Old Testament (from which the theological idea of "conversion" was ultimately developed), see on Amos 4:6.

with all your heart with the entire force of your moral purpose. The Deuteronomic phrase is "with all your heart and with all your soul" (Deuteronomy 6:5, and elsewhere), i.e. with the intellect and the affections combined [39]; but the heart alone is often mentioned (e.g. 1Sa 12:20; 1 Samuel 12:24; Jeremiah 29:13; and, as here, with turn, 1 Samuel 7:3; Jeremiah 24:7). The heart is in Hebrew psychology not (as with us) the organ of the affections, but the organ of the intellect (see e.g. Hosea 7:11); here, the organ of moral purpose and resolve.

[39] See the writer's Commentary on Deuteronomy, pp. 21 n., 73, 91.

with fasting, and with weeping, and with wailing] i.e. with grief for sin, of which these are to be the external signs. On fasting, as a mark of penitence, see on Joel 1:14: on weeping, as its concomitant, Judges 20:26; Psalms 69:10; Zechariah 7:3; cf. 2 Kings 22:19; Isaiah 22:12; Ezra 10:1.