The quotation is from Jeremiah 31:15-17. We rarely hear the rest of the citation which contains a promise and hope. "Thus says the LORD: “Keep your voice from weeping, and your eyes from tears; for there is a reward for your work, says the LORD: they shall come back from the land of the enemy; there is hope for your future, says the LORD: your children shall come back to their own country.”
“…chains can’t bind the hopefulness.
And the bars can’t block the means of grace.
And the distance that might separate,
Cannot defeat the prayers…
So fellow prisoners, remember,
That we may know captivity.
But there’s a purpose in the Calling,
For it is the Lord who sets the prisoners free.”
As with all the songs on his album Soul Anchor, Card uses citations from Hebrews. This one is based on Hebrews 10:34 and 13:3 which call us to “Remember those who are in prison, as though you were in prison with them; those who are being tortured, as though you yourselves were being tortured.” (Hebrews 13:3) because we possess “something better and more lasting.” (Hebrews 10:34)