Matthew Poole and continuators on John 19:34

34 But one of the souldiers with a spear pierced his side , and forthwith came there out, blood and water.

But one of the Souldiers to make sure of him, pierced his side, out of which it is said, that there presently came forth blood, and water: That there should come out blood is no wonder, nor yet that there should come forth water. Blood being congealed, it is ordinary to see water on the top of the Vessel where it is. And besides, Anatomists tells us, that in the hollow part of the breast, there are watery, as well as bloody humours in the membrane that incompasseth the heart, which being pierced, and the water let out, the living creature dyeth necessarily. But yet in regard of the next words, He that saw it bare record, and he knoweth that he saith true, &c. most Divines think, that there was some mystery in this water and blood, which came out of Christs side pierced. Some would have the two Sacraments of the Gospel, signified by this water and blood. Christ 1 Iohn 5.6. is said to have came by water and blood; That is, say Interpreters, be brought in a true expiation of sins by his blood, and the laver of Regeneration, washing the Soul from its filthiness: And thus he proved the true Antitype, answering the Iewish Types in Sacrifices, and divers washings.