Father Raniero Cantalamessa via ZENIT:
The Gospel for the solemnity, drawn from Jesus' farewell discourses, deals with three mysterious subjects which are inextricably united, the Father, the Son, and the Holy Spirit: "When the Spirit of truth comes, he will lead you into the whole truth. … All that the Father has is mine" -- the Son! Reflecting on these and similar texts the Church arrived at its faith in the Trinitarian God.
Many ask: But what is this puzzle of three who are one and one who are three? Would it not be easier to believe in a God who is just one, as the Muslims do? The answer is simple. The Church believes in the Trinity, not because it likes to complicate things, but because this truth has been revealed by Christ. The difficulty of understanding the mystery of the Trinity is an argument in favor of, and not against, its truth. No man left to himself would have ever come up with this mystery.
After the mystery has been revealed to us, we intuit that, if God exists, it can be no other way: one and three at the same time. There can only be love between two or more persons; if therefore "God is love," there must be in God one who loves, one who is loved, and the love that unites them.
Christians are monotheists; they believe in a God who is one, but not solitary. Who would God love if he were absolutely alone? Perhaps himself? But then his love would not be really love, but rather egoism or narcissism.
I would like to consider the great and formidable teaching about life that comes to us from the Trinity. This mystery is the maximum affirmation that there can be both equality and diversity: equal in dignity but different in characteristics. And is this not the most important thing that we must learn if we are going to live well in this world? That we can be, that is, different by the color of our skin, because of culture, sex, race and religion, and yet enjoy equal dignity as human persons?
This teaching has its first and most natural field of application in the family. The family must be an earthly reflection of the Trinity. It is made up of persons of different sex (man and woman) and age (parents and children) with all the consequences that derive from these differences: different sentiments, different attitudes and tastes. The success of a marriage and a family depends on the measure by which this diversity knows how to tend toward a higher unity: unity of love, intentions and collaboration.
It is not true that a man and a woman must have the same temperament and gifts; that for them to agree, they must both be either cheerful, vivacious, extroverted and instinctive, or both introverted, quiet and reflective. Indeed we know what negative consequences can follow, even at the physical level, from marriage between relatives within a restricted circle.
Husband and wife do not have each to be the "better half" of the other in the sense of two halves perfectly equal, as an apple cut in two, but in the sense that one is the missing half of the other and the complement of the other. This was God's intention when he said: "It is not good for man to be alone; I will make him a help similar to him" (Genesis 2:18). This all presupposes the strength to accept the difference of the other, which is the most difficult thing for us to do and in which only the most mature marriages succeed.
From this we also see how erroneous it is to consider the Trinity a mystery that is remote from our lives, one to be left to the speculation of theologians. On the contrary, it is a mystery that is very close to us. The reason is very simple: We were created in the image of the Trinitarian God, we bear this imprint and we are called to realize the same sublime synthesis of unity and diversity.