Thomas Aquinas Commentary Jeremiah 31:21-22

"Set thee up waymarks, make thee guide-posts; set thy heart toward the highway, even the way by which thou wentest: turn again, O virgin of Israel, turn again to these thy cities. How long wilt thou go hither and thither, O thou backsliding daughter? for Jehovah hath created a new thing in the earth: a woman shall encompass a man." — Jeremiah 31:21-22 (ASV)

v.21a

Here, instruction is given to the penitent: establish for yourself a watchtower (speculam), so that you may consider the prosperity that has been announced, or so that you may consider the way by which you may return. The word bitterness refers to concern for the return. The word direct means to consider the way by which you came, so that you may return by it.

Alternatively, a better interpretation is: establish for yourself a mirror (speculum) of contemplation; bitterness for past sins; and turn to the straight way, that is, to the way of justice on which your fathers walked. As it is written, Remember from where you have fallen; repent, and do the first works (Revelation 2:5).

v.21b-22

Here, their calling back to their own land is put forth.

1. The call to return is given: return... how long will you be unrestrained in your delights, O wandering daughter? This is said in regard to those who, absorbed by the delights of the Chaldeans, did not wish to return to the promised land. These are rightly called women because of their effeminacy. As it says above: Though you have fornicated with your many lovers, still, return to me, says the Lord, and I will take you (Jeremiah 3:1).
2. The reason for calling them back is given from the Incarnation of Christ, which should induce everyone to turn from their delights: for the Lord has created a new thing upon the earth. This is a new thing because that conception occurred only through the agency of divine power. A woman, referring to the condition of the fragile sex, shall encompass in her womb a man—Christ, who was perfect in knowledge and grace from the beginning of his conception. For this reason, you should hasten to the land in which this new thing must come to pass: put on the new man, who, according to God, is created in justice and the holiness of truth (Ephesians 4:24). Behold the man, the Orient is his name, he shall rise under him; and he shall build a temple to the Lord (Zechariah 6:12).