“I will fill the descendants of David and the other people of Jerusalem with the spirit of mercy and the spirit of prayer. They will look at the One whom they stabbed to death and they will mourn for Him like those who mourn for an only child ; they will mourn bitterly like those who have lost their first born son” (Zechariah 12).
St John in the episode of the pierced Heart (see above at the beginning), quotes a few significant words from the passage of the prophet Zechariah. And the words which follow in this passage announce already implicitly the true identity of the One who will be pierced : “Only Child”, “First Born”.
Heart of Jesus, pierced by the spear, have mercy on us.