In book one, chapter VIII, of The Doctrine & Discipline of Divorce, it is written:
Upon these principles I answer, that a right beleever ought to divorce an idolatrous heretick unlesse upon better hopes: however, that it is in the beleevers choice to divorce or not.
The former part will be manifest thus; first, an apostate idolater whether husband or wife seducing was to die by the decree of God, Deut. 13. 6, 9. that mariage therfore God himself dis-joyns: for others born idolaters the morall reason of their dangerous keeping and the incommunicable antagony that is between Christ and Belial, will be sufficient to enforce the commandment of those two inspir’d reformers, Ezra and Nehemiah, to put an Idolater away as well under the Gospel.
The latter part, that although there be no seducement fear’d, yet if there be no hope giv’n, the divorce is lawfull, will appeare by this, that idolatrous marriage is still hatefull to God, therfore still it may be divorc’t by the patern of that warrant that Ezra had; and by the same everlasting reason: Neither can any man give an account wherefore, if those whom God joyns, no man may separate, it should not follow, that, whom he joyns not, but hates to joyn, those man ought to separate: but saith the Lawyer, that which ought not have been don, once don, avails. I answer, this is but a crotchet of the law, but that brought against it, is plain Scripture.
I tried to decode Milton, I read it:
[...]: Neither can any man give an account why, if those whom God joyns, no man may separate, it should not follow, that, whom he [God] does not join, but hates to join, those man ought to separate: but says the person in favour of the canon law, that which ought not have been done, once done, avails. I answer, this is but a crotchet of the law, but that brought against it, is plain Scripture.