If civil divorce remains the only possible way of ensuring certain legal rights, the care of the children, or the protection of inheritance, it can be tolerated and does not constitute a moral offense.
As to why divorce is required, there’s a relatively simple answer. Canon Law (canon 1676) requires tribunal judges to be sure that reconciliation is not possible between the spouses before proceeding with an annulment case. Obtaining a civil divorce is a sign that reconciliation is not possible.
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