For today's Christians, for whom the Trinity is still an enigmatic reality, the gospel of John aims at transmitting what is essential in faith and in profound relationship with God who is the Father, the Son and the Holy Spirit. The present research reveals that the concrete theme of Worshiping of the Father in Spirit and Truth involves the very core and essence of our Christian faith and its far-reaching implications for post-Easter believers. The study shows - through a lucid exegetico theological analysis of the key-words of the theme: o path, r, pneu/ma and avlh, qeia - how the gospel makes plain that these key-words are not only reciprocally interconnected but strictly linked with the person of Jesus. Moreover, they are not just the keywords but they refer to the living persons: the Father, the Spirit and the Truth, that is to Jesus in person and to the truth of his revelation. Therefore, such an approach to the theme of Worshiping the Father in Spirit and Truth, within the Johannine account, has to be seen in terms of the relationships among the Father, the Son and the Holy Spirit. In other words, it is the worship of God who is one in three distinct persons. The study explicitly stresses that the above-mentioned relationships among the Father, Jesus and the Holy Spirit are directed towards the world. The indwelling God, Three-in-One in the post-Easter believers and the abiding of these believers in the Father and in the Crucified-Risen Jesus is experienced now in worship by means of the activity of the Spirit. It is precisely through the Spirit that the Father and the Crucified-Risen Jesus invite believers to the lasting relationship with them, which means to worship in its deepest sense.