Here starts the central and most heartfelt part of the whole book. Jeremiah wrestles himself loose from his imprisonment to grievous memories. He starts to bring thoughts to mind that give hope.
The first thought is of the great love and mercies of the Lord. These are the great love and mercies that he revealed when he made his covenant at Horeb, and that he has shown in many ways to his people ever since. Jeremiah had been afraid that the Lord's love has now come to an end (verse 18). But here he remembers that a remnant of Judeans has still remained—not everyone was “consumed.” It can only be because of God’s great love that they were not completely destroyed.
Then Jeremiah remembers that the Lord has promised to never forget his covenant forever (Leviticus 26:42; Deuteronomy 4:31). He realizes that there is no end to the Lord's great love and compassion, because his faithfulness is great—as his Word promises.
For these reasons, the Lord is still Jeremiah’s “portion.” For him, as the son of a priest (Jeremiah 1:1), this has special significance. The Levites did not receive their own land in Canaan, but they were promised by the Lord that he was their “portion” (Numbers 18:20; Deuteronomy 10:9). He was the “land” from which they could live.
Jeremiah will therefore “wait” (or “hope”) for the Lord. Waiting or hoping in the Scriptures is not an act of uncertainty, but of certainty that the Lord will answer.
21 But this I call to mind, and therefore I have hope: