Thomas Aquinas Commentary Jeremiah 4:1-2

"If thou wilt return, O Israel, saith Jehovah, if thou wilt return unto me, and if thou wilt put away thine abominations out of my sight; then shalt thou not be removed; and thou shalt swear, As Jehovah liveth, in truth, in justice, and in righteousness; and the nations shall bless themselves in him, and in him shall they glory." — Jeremiah 4:1-2 (ASV)

Here, the prophet gives the arguments for their return:

1. Arguments drawn from the benefits promised to those who return.
2. Arguments from the punishments threatened to those who defy him, beginning at Jeremiah 4:3: thus says the Lord.

Regarding the first point on promised benefits, there are two aspects.

First, he shows the manner of their return: if you return from idols, to turn back to me. This means that if you decide to return, you must be converted in your whole heart. Or, if you return from captivity, you must come back in repentance. As Isaiah says, If you seek, seek! Turn back, and come! (Isaiah 21:12).

Second, he shows the three fruits of conversion:

1. The first fruit is security: if you remove your offences—that is, the idols by which you continually offend and provoke me to wrath—you will not be moved from your native land. As the Psalm says, Those who trust in the Lord are like mount Zion; he who dwells in Jerusalem shall not be moved forever (Psalms 124:1).
2. The second fruit is holiness within themselves: he has sworn: as the Lord lives. This means swearing by the living God and not by dead idols. The oath must be taken in truth, meaning truthfully on the part of the one swearing, not insincerely or with intent to deceive. It must be taken in judgment, referring to the reason for the oath, so that they do not swear rashly but with careful prior consideration. And it must be taken in justice, referring to the subject of the oath, ensuring it is just and lawful. As Isaiah says, He that swears in the earth shall swear by God, amen (Isaiah 65:16).
3. The third fruit is the spread of religion among the nations: and the nations shall bless the Lord, seeing His benefits in you. As the Psalm says, Bless our God, you nations! (Psalms 65:8).