Remain with God in the Calling You Received
Paul gives a general rule: conversion does not require believers to erase every social or ethnic circumstance of their calling. Circumcised and uncircumcised believers are not to treat bodily status as the basis of acceptance. Enslaved believers should not imagine that their social condition prevents belonging to Christ, and free believers must remember they are Christ’s servants.
The slavery language must be handled responsibly. Paul speaks pastorally to people living inside a real slave system; he is not declaring slavery morally ideal. Verse 21 may even encourage taking freedom when the opportunity exists, depending on how the Greek is read.