God does not tell Jeremiah that he will rescue his people from that captivity. Instead, he tells Jeremiah what the nation of Israel should focus on in that less-than-ideal set of circumstances.
As Keller explains, there is no such thing as “objective” abandonment for Christians. Only Christ was actually abandoned by the Father. Therefore, all that remains is “subjective” abandonment. In other words, though we may feel abandoned by God (feel = subjective), it is never the case (objective).
Nietzsche, an adamant atheist and outspoken critic of Christianity, ironically said, “Truth is hard.” It is. Let it pierce me, crush me, kill me. But don’t lie to me and others.