The word "chains" is a metaphor that Paul uses to indicate that he is in prison, but it is also likely that he was literally attached to a chain. Alternate translation: "Remember me and pray for me while I am in prison" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "grace" stands for God, who shows grace or acts kindly to believers. Alternate translation: "I pray that our Lord Jesus Christ would continue to act graciously toward you all" (See: [[rc://en/ta/man/translate/figs-metonymy]])