When the Spirit of truth comes, he will guide you into all the truth.
What we find difficult to understand we tend either to ignore or change into something we can understand. Now few things are more difficult to comprehend than the Christian doctrine of the Trinity, the doctrine that God is one in substance but three in Persons - the one God is Father, Son and Holy Spirit.
It is tempting to ignore or simplify this doctrine, and just relate to God without thinking of Him as three Persons, or relate to the Father and the Son and even the Holy Spirit as three divine beings, not worrying about how to unify them. Christians have always been tempted to go for one or other of these options, whether it be in theological accounts or spiritual practice.
Yet neither will do and the Church in its creeds makes clear that we need to keep both the oneness and threefoldedness of God in our minds and hearts, in what we say of God and of God's relation to us and our relation to God. That God is Trinity is the fundamental experience of God which Christians have. It is an experience which arises from the encounter with the person of Jesus Christ and in the encounter with the Holy Spirit.
It is not a doctrine which has been thought up solely in the speculations of theologians, but is the understanding of God which arises from the Christian experience of the saving action of the God who created and sustains the world. To ignore or simplify the Trinity is to ignore or simplify Christian experience of God. It is to rob ourselves of the richness of the Christian encounter with God.
Now we are perhaps not helped by many of the formulae we use in confessing our faith in the Trinity. Every day Christians will begin their prayers or other activities making the sign of the Cross - 'In the name of the Father and of the Son and of the Holy Spirit.' Every day Christians praise God by saying, ' Glory be to the Father and to the Son and to the Holy Spirit.' The Trinity seems to be a list of divine Persons rather than one God.
Of course that is not the intention of these prayers, and instead they are meant to make clear the full divinity of all three Persons. Yet in the minds and spiritual practice of Christians, these formulas can have the effect of weakening a sense of the unity of God.
Another ancient formula, however, expressive of the Church's faith is
one God and Father from whom all things are, and one Lord Jesus Christ through whom all things are, and one Holy Spirit in whom all things are.
This is the pattern for the prayers of the liturgies of the Church and manifests the unified action of the Trinity. The world in its creation and redemption comes from the Father and returns to the Father, comes through the Son and returns through the Son, comes in the Spirit and returns in the Spirit.
Each of us is caught up in this movement from and to the Father, through the Son, in the Holy Spirit. Every prayer that we make and every activity we undertake is directed to the Father, through the Son, in the Holy Spirit. Understanding the Trinity in this way makes it easier for us to relate more fully to God as Trinity.
The readings for today's feast themselves manifest this threefold but unified action of the Trinity. In John's Gospel Jesus promises that the Spirit with enlighten the disciples in the truth which comes from the Father, through the Son:
When the Spirit of truth comes he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come. He will glorify me, for he will take what is mine and will declare it to you. All that the Father has is mine; therefore I said that he will take what is mine and declare it to you.
In his letter to the Romans, Paul teaches that the theological virtues of faith, hope and love, which mark the redemptive life of grace, draw us back to the Father, are given through the Son, and are manifested in the presence of the Holy Spirit:
Therefore, since we are justified by faith, we have peace with God through our Lord Jesus Christ. Through him we have obtained access to this grace in which we stand, and we rejoice in our hope of sharing the glory of God ... and hope does not disappoint us, because God's love has been poured into our hearts through the Holy Spirit who has been given to us.
In our encounter with God as Trinity we are in this way drawn into the richness and glory of God's own life.
Of course those who are not Christians are themselves subject to the creative and redemptive activity of the Trinity, but central to Christian faith is the experience that through the life, words and actions of Jesus Christ the Trinitarian nature of God is revealed to us. Since we as human beings live the more fully the more we have understanding of how things are, so an explicit awareness of the Trinitarian nature of God and the shaping of our minds and actions by this truth enables us to live a richer and more wondrous human life in the here and now.