Gospel (Jn 16:12-15)
At that time Jesus said to his disciples:
“I have yet many things to say to you, but you cannot bear them now. 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 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.”
At the Last Supper, Jesus reveals to the Apostles the deepest truths about himself and his relationship to the Father and the Holy Spirit, while assuring them that they will not be left alone. They will have the help of the Holy Spirit, who will continue his mission by guiding the Church throughout time.
The Apostles have been witnesses to Jesus’ preaching and actions, as well as to his filial dialogue with God, whom he always addresses as “Father,” even sometimes using the young child’s term abba, “daddy,” "papa" (cf. Mk 14:36). Now he speaks to them about the help they will receive from the Holy Spirit: “for he will take what is mine and declare it to you” (v. 14). The action of the Spirit upon the Church does not consist in raising up or teaching things different from what Christ declared—since the truth does not change over time, nor vary with people’s opinions or viewpoints. Rather he will assist the full understanding of all that the Son heard from the Father and made known to them (cf. v. 15). Jesus had already announced to them that “the Counselor, the Holy Spirit, whom the Father will send in my name, he will teach you all things, and bring to your remembrance all that I have said to you” (Jn 14:26). And now he adds: “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” (v. 13). His mission will be to guide us to the truth amid the new and changing situations in history and people’s lives, with the focus always on what Jesus has taught us.
Jesus speaks with naturalness about the Father and the Spirit as Persons distinct from himself and from one another, while implying that they share in the same reality: “All that the Father has is mine” (v. 15). The Spirit “will take what is mine and make it known to you” (v. 14). There is only one God, a single divine nature, subsisting in three distinct persons, the Father, the Son, and the Holy Spirit. The Catechism of the Catholic Church employs the formula of the ancient profession of faith called the Quicumque when it states: “Now this is the Catholic faith: We worship one God in the Trinity and the Trinity in unity, without either confusing the persons or dividing the substance; for the person of the Father is one, the Son’s is another, the Holy Spirit’s another; but the Godhead of the Father, Son and Holy Spirit is one, their glory equal, their majesty coeternal.”
This truth of our faith is not a beautiful, but distant reality. Rather it speaks to us of our personal relationship with God and with each of the divine Persons. As Pope Francis reminds us: “through baptism, the Holy Spirit has placed us in the heart and the very life of God, who is a communion of love. God is a ‘family’ of three Persons who love each other so much as to form a single whole. This ‘divine family’ is not closed in on itself, but is open. It communicates itself in creation and in history and has entered into the world of men to call everyone to form part of it. The trinitarian horizon of communion surrounds all of us and stimulates us to live in love and fraternal sharing, certain that where there is love, there is God.”
We have been created in the image and likeness of God. Thus it is a part of our own nature to foster unity and reciprocal love for God and our fellow men and women, in the great family of the world and the Church, in social and domestic relations, in friendship and the workplace. “The Feast of the Most Holy Trinity invites us to commit ourselves in daily events to being leaven of communion, consolation and mercy.”
 Catechism of the Catholic Church (Athanasian Creed: DS 75; ND 16), no. 266.
 Pope Francis, Angelus Address, 22 May 2016.