By the gift of the Holy Spirit at Pentecost, the church was born and set out upon the pathways of the world, yet a decisive moment in her taking shape was certainly the institution of the Eucharist in the Upper Room. Her foundation and wellspring is the whole Easter Triduum, but this is as it were gathered up, foreshadowed, and concentrated for ever in the gift of the Eucharist. With it Jesus brought about a mysterious "oneness in time" between that Triduum and the passage of the centuries.