"Chains in Christ" here is a metonym for being in prison for the sake of Christ. "Came to light" is a metaphor for "became known." Alternate translation: "It became known that I am in prison for the sake of Christ" (See: [[rc://en/ta/man/translate/figs-metaphor]])
This can be stated in active form. Alternate translation: "the palace guards and many other people in Rome know that I am in chains for the sake of Christ" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Here Paul uses the preposition "in" to mean "for the sake of." Alternate translation: "my chains for the sake of Christ" or "my chains because I teach people about Christ"