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It is written that when the side of Jesus was pierced "He shed thereout blood and water." This has a mystical meaning. For Himself had said, "Out of His belly shall flow rivers of living water." ... Yet it might be understood also as prefiguring the twofold grace of baptism, one that which is given by the baptism of water, the other that which is sought through martyrdom in the outpouring of blood, for both are called baptism.
— TYRANNIUS RUFINUS