"whether he was married or unmarried, slave or free, when he was called"
# he was called
You may need to make explicit who called and use an active verb. Alternate translation: "God called him" (See: [[rc://en/ta/man/translate/figs-activepassive]] and [[rc://en/ta/man/translate/figs-explicit]])
# called
called to believe in Christians
# let each one remain
"each one should remain." That is, each one should remain slave, free, married, or unmarried, as he was when he first believed in Christ.