404. And a third of the sea became blood. This symbolically means that general truths had all been falsified in them.
A third means, symbolically, all (no. 400). Blood symbolizes the falsification of the Word's truth (no. 379). The sea symbolizes the church in people concerned with its external elements and caught up in faith alone (nos. 398, 402). General truths are falsified among such people because they are concerned with those truths alone, as they do not know the particulars of that faith, as the clergy do. It is because of those general truths in them that they appear in the spiritual world to be at sea. That is because waters symbolize truths (no. 50), and the sea is the general receptacle of them (no. 238).