I can only imagine the ups and downs of Jesus' disciples during the first Easter season. They were up during Jesus' public ministry and down when he was crucified. They were elated at His Resurrection and those precious times when He spoke, ate, and traveled with them. This led to the events we remember today His ascension. I can't help but think that as they watched Jesus disappear into the clouds a "here we go again" thought must have passed their minds, but this time is different, they were strengthened because Jesus had delivered on His Resurrection promise. They needed to believe, as they gathered in prayer, that the Holy Spirit would come to them and they could begin to bring the gospel message to all the nations.
As we wait with the disciples for Pentecost Sunday and reflect on these Easter events we can truly see a trinitarian connection. Jesus' resurrection is God's triumph over sin and death. His ascension to be the Father is where Jesus remains now until He comes again in His glory. He intercedes to the Father on our behalf. The third part of this trinitarian time is going to happen at Pentecost when the Father and Son will pour out their Spirit, a Spirit of love, a Spirit of strength that allows us in our most imperfect way to follow the Son in doing the Father's will.
This mystery of the Trinity is reflected in the mission of the Church as the Dogmatic Constitution of the Church states:
4. When the work which the Father gave the Son to do on earth was accomplished, the Holy Spirit was sent on the day of Pentecost in order that He might continually sanctify the Church, and thus, all those who believe would have access through Christ in one Spirit to the Father. He is the Spirit of Life, a fountain of water springing up to life eternal. To men, dead in sin, the Father gives life through Him, until, in Christ, He brings to life their mortal bodies. The Spirit dwells in the Church and in the hearts of the faithful, as in a temple. In them He prays on their behalf and bears witness to the fact that they are adopted sons. The Church, which the Spirit guides in way of all truth and which He unified in communion and in works of ministry, He both equips and directs with hierarchical and charismatic gifts and adorns with His fruits. By the power of the Gospel He makes the Church keep the freshness of youth. Uninterruptedly He renews it and leads it to perfect union with its Spouse. The Spirit and the Bride both say to Jesus, the Lord, "Come!"
Thus, the Church has been seen as "a people made one with the unity of the Father, the Son and the Holy Spirit." Lumen Gentium
We must remember some of the names of the faithful that make us part of the mystery of the Trinity. We are a people of God, The Body of Christ, and Temples of the Holy Spirit; as Richard P. McBrien points out in "The Church, The Evolution of Catholicism"