First, Jesus being pierced through the heart is very interesting. John emphasizes that the day Jesus died was the day of preparation for the Passover. This does not conflict with the Synoptic Gospel which merely state that Jesus celebrated Passover with his disciples on the night on which he was betrayed, not that it was necessarily the day that other people were celebrating it. In any case, if this is so, then Jesus would have been on the cross, according to John, at the precise time that the Passover Lambs were being slaughtered. According to Rabbinical literature, Lambs killed for the Passover were slaughtered at the time of Christ by being pierce through the heart and then letting the blood be drained. The parallel then with Jesus is obvious. Some have also noted that Lambs were often roasted on cross beams that resemble the cross.
What is most interesting to me is the parallel between the passion narrative and the Passover liturgy that has been handed down to us. First, I will make a historical and exegetical move that I think is not only theologically justifiable (God is the author of Scripture, so we can read each passage in light of the whole Bible), but historically as well. It would be my contention that John when he wrote his Gospel was completely aware of the other Gospels and intended his Gospel to be read in light of the other ones. Here I of course go against the consensus of NT scholarship since Bultmann, but I think it justifiable.
Why do I think this? A number of reasons. 1. John wrote his Gospel long after the Synoptic Gospel had been written and therefore its is highly unlikely that he would not have known them. As Richard Bauckham showed in A Gospel for All Christians, it is absurd to think that the Synoptic Gospels (or John for that matter) were written for individual communities and therefore would have been circulated immediately. 2. As Richard Bauckham also shows in Jesus and the Eye Witnesses, John is aware of the Petrine witness present in Luke and Mark, since he uses the literary technique of "inclusio of eye witness." The inclusio of eye witness is a literary technique of the first and second centuries AD, where the author would make the first and last disciple (Bauckham uses various philosophers' biographies to make his point) mentioned in the biography the person who served as the eye witnesses to story being told. Mark has one involving Peter, Luke has one involving Peter and then a wider one involving the women disciples of Jesus, whom Bauckham thinks are Luke's primary source (BTW, Matthew doesn't have one!). John has one with Peter- meaning he acknowledges the Petrine witness in the Synoptic tradition that he is well aware of- but then makes his own (the beloved Disciple) wider than Peters, meaning he both is acknowledging, commenting on and expanding on the Petrine witness. If that is correct (which I think I have made a strong historical and theological case for), then John intends his passion narrative to be read in light of and in conjunction with, the Synoptic Gospels.
Back though to the Passover liturgy. The Passover liturgy in the first century (as far as we can tell!) had 4 parts. Each part involved a separate cup to be drank and a prayer to be said. Bear in mind, this is why the Disciple kept on falling asleep in the garden, they had consumed alot of wine! (Wine in antiquity was frequently watered down, but still that's alot). Anyways, it tends to be the consensus of scholars (Joachim Jermias has not been rejected on this point) that Jesus instituted the Lord's Supper on the third cup, the "Cup of Blessing." There is further evidence of this from Paul's remark in 1 Cor. "is not the Cup of blessing that we bless . . ." referring to the cup used in the Lord's Supper.
If that is the case, then what is interesting is that there is no fourth cup after the institution of the Lord's Supper in the Synoptic Gospels. Well, one could say, there is no first and second either. Nevertheless, we're really not told what happened before the institution of the Sacrament (except for what the conversation was about), but we are told what happened afterwards. Mark tells us that they sang some hymns- which is what you were supposed to do in the 4 part liturgy after the fourth cup. But then, it seems that there's no fourth cup, since it would probably be mentioned along with the hymn singing activity. There's further evidence also. Remember, Jesus says that he won't drink of the "fruit of the vine" until he drinks it anew in the kingdom of God. This would mean that he won't drink the fourth cup.
Now, what does John tell us that's unique? When Jesus is on the cross about to die, he does finally drink the fourth cup. He asks for a drink and he consumes wine on the cross. Read in light of the other narratives, we discern several things. First, the kingdom (as Chemnitz might say, the "kingdom of grace") comes when Jesus has fulfilled the Father's will by dying for our sins. Secondly, it means that the cross completes a new Passover liturgy and therefore the new exodus from sin, death, the devil and the law. After all, you need sacrificed body and blood to enact the new Passover. Jesus' body and blood as they are presented to us in the Lord's Supper are sacrificed body and blood, in that in the OT sacrifice meant the separation of blood from the body of the animal (see Lev. 17). In this, the cross along with the meal of the New Testament, complete one event of the New Passover and the new exodus.