When speaking with Catholics and non-Catholic Christians, one can almost always assume that God is understood as a Trinity of persons. For the Jews, our forefathers in faith, this basic understanding of God is untenable. Therefore, when Christ revealed that God is not only Father (He told His hearers to call him "Abba"), but also includes Christ Himself as the Son and the existence of the Spirit, the majority of the Jews of our Lord's time were incredulous at such a claim. The idea of God sharing the same substance but in three distinct persons was a complete departure from the Jewish understanding of God's nature. Moreover, the claim that any man could make himself to be God's son was blasphemous to the Jews.
The gospel passage relates this mystery and the relationship between the three persons of the Trinity. Jesus reveals some of the characteristics of that inner relationship and provides us with insights into how we should interact, since we are made in the image and likeness of God. Jesus' words remind us that the Trinity is a communion of persons. As such, the Trinity always acts in perfect unity. Jesus describes how the Spirit will communicate to the apostles that which belongs to the Father and to the Son. Whenever one person of the Trinity acts, the other two persons are surely conjoined to that divine activity.
Similarly, this concept of the Trinity as a communion of persons (communio personarum) reveals our vocation as believers to act in communion with one another. This is particularly important to recall in an age where society glorifies individualism and a preference for human activity that is insular and avoids person-to-person contact. Imagine that in most of the United States, one could accomplish most of their Saturday-morning errands without ever speaking to another human person. A visit to the bank ATM, the self-checkout line at the grocery store and the pay-at-the-pump gas station (with or without automated carwash) alienates us from human contact. The proliferation of iPods and similar devices allows us to escape from human interaction. We observe many teens listening to music on earphones while riding in a car with their parents, rather than developing conversational skills and fostering family communication. In business, we often find ourselves preferring to write e-mails or leave voicemails rather than speak directly to another person. While none of these technological advances are inherently evil, of course, they do tend to de-humanize us by providing us with reasons not to interact with one another. And yet, we are called to reflect how God interacts within Himself. In other words, we were made for one another and we need each other. When modern man becomes alienated from his fellow man, ideas like the common good or public decency or good manners are devalued.
As we meditate upon this fundamental mystery of our faith, we do well to ask our gracious God to help us live in a manner that best reflects our vocation to live in communion with one another never forgetting that in doing so we also strive to live in the image and likeness of our Trinitarian God.