A.T. Robertson Commentary 1 Corinthians 7:15

"Yet if the unbelieving departeth, let him depart: the brother or the sister is not under bondage in such [cases]: but God hath called us in peace." — 1 Corinthians 7:15 (ASV)

Is not under bondage (ου δεδουλωτα). Perfect passive indicative of δουλοω, to enslave, has been enslaved, does not remain a slave. The believing husband or wife is not at liberty to separate, unless the disbeliever or pagan insists on it. Wilful desertion of the unbeliever sets the other free, a case not contemplated in Christ's words in Mt 5:32; 19:9. Luther argued that the Christian partner, thus released, may marry again. But that is by no means clear, unless the unbeliever marries first.

But God hath called us in peace (εν δε ειρηνη κεκληκεν ημας or υμας). Perfect active indicative of καλεω, permanent call in the sphere or atmosphere of peace. He does not desire enslavement in the marriage relation between the believer and the unbeliever.