“The mystery of the Most Holy Trinity is the central mystery of the Christian faith and of Christian life,” says the Catechism of the Catholic Church.
It is because of the centrality of this teaching that a person enters the Church through baptism and faith in the “name of the Father, the Son and the Holy Spirit”. The omission of an “s” at the end of “name” to retain the singular is deliberate. The Most Holy Trinity is one God, but three Persons.
The Trinity was expounded perhaps most profoundly through the teachings of Our Lord in St John’s Gospel. Yet it sometimes remains hard to grasp this side of eternity. Just how can one at the same time be three? The Church has always found ways to explain the mystery. St Boniface, for instance, taught the Trinity to tree-worshipping German pagans by using triangular points of their deities to denote each of the three truly divine Persons.
Later, many of the Christians of medieval Europe adopted the Scutum Fidei, the “Shield of the Trinity”, to express the doctrine, using the same triangular points but this time each linked by a bridge to a node at the centre marked with the word “God”.