First, history: Baruch, a scribe who had been taken to Babylon with the first exiles, has learned of the destruction of the Temple.
Baruch attempts to console and to instruct.
Israel saw the exile as a justifiable punishment for its sin, for its failure to do what the Lord had instructed to, to live in the ways that the Lord had intended for them to live. Yet, despite their guilt, God will show them mercy. (Source: Abingdon: NISB)
Baruch addresses Jerusalem (the left-behinds, the witnesses to the destruction), "Arise, O Jerusalem, stand upon the height; look toward the east, and see your children gathered from west and east at the word of the Holy One.... For God will lead Israel with joy, in the light of his glory, with the mercy and righteousness that come from him."
Now, the present: We have sinned or lived among people that sinned or both. We have seen the consequences of those sins. And we can sometimes admit that we did deserve those consequences. But, Advent is not a time to dwell on what-might-have beens.
Baruch's words of comfort for an ancient people, scattered, hurt, suffering from losses of status and property can still speak to us. God still comes with mercy and righteousness.