Well, that student is not alone, because this concept places us, once again, in the area of “mystery.” As you can see, these “mysteries” all seem to emerge in large right after Easter, the greatest mystery of all. It is our faith in that mystery of Jesus’ life, death and resurrection that allows us to walk once again in the complete faith of our spiritual journey. So in rapid fashion after the Easter season, we celebrate the mysteries of Pentecost, the Most Holy Trinity, Corpus Christi (the Body and Blood of Christ), and the Sacred Heart of Jesus.
The early Christians had a difficult “doctrinal transition” to make: from believing in the One God, to believing in this same One God formed in Jesus the Christ. So they developed “Trinitarian language” to preserve both of those truths, as well as a third truth: that the Spirit of Jesus kept the presence of God constantly in our midst. In fact, it is this Spirit of God who, through baptism, dwells within the believer.
In today’s Gospel, Jesus conveys this truth, when he commands his disciples to baptise and teach “in the name of the Father, and of the Son, and of the Holy Spirit” (Mt 28:16-20). The early Church Fathers preserved this dogmatic belief in “One God but Three Divine Persons in that One Godhead,” by wrapping that belief in a dogmatic Creed. It still remains a “mystery,” and the poverty of our human understanding shows the gap between the Human and the Divine. So the answer to that student’s question above is “no, there is no quick way to absorb this concept, except the way of faith!"
What an incredible gift is the theological virtue of faith, the free assent of the believer to the whole truth that God has revealed! The mystery of the Trinity in itself is inaccessible to the human mind, and is the object of faith only because it was revealed by Jesus Christ, the divine Son of the eternal Father. The faith of all Christians rests on the Trinity.