# Brothers

Here this means fellow Christians, including both men and women.

# whatever situation he was in when he was called

"whether he was married or unmarried, slave or free, when he was called"

# he was called

"God called him" 

# 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.

# with God

"as a person responsible to God"