Thomas Aquinas Commentary Jeremiah 3:19

"But I said, How I will put thee among the children, and give thee a pleasant land, a goodly heritage of the hosts of the nations! and I said, Ye shall call me My Father, and shall not turn away from following me." — Jeremiah 3:19 (ASV)

1. Here, he gives the reason for their being called back.

1. He poses the question: how? That is, how is it possible that I should bestow so many good things upon you, when you languish in so many sins? Among the sons, that is, among a multitude of sons; the hosts of the nations, that is, where armies have gathered since ancient times, as they do even to this day, because of its allurements: they set at naught the desirable land (Psalms 106:24). The lines have fallen to me in goodly places, for my inheritance is goodly to me (Psalms 16:6).
2. He gives the response: and I said, that is, foreseeing the good that you will do, I promise these things to you. He will call upon me: you are my father, my God and the support of my salvation (Psalms 89:26).