Is belief in the Trinity irrational?

At every Sunday Mass we profess that we believe in the Holy Trinity,

in the Father, the Son, and the Holy Spirit.

In fact, you could even say this is the central claim of Christianity.

So, every Christian begins the Christian life in baptism,

being baptized in the name of the Father,

and of the Son, and of the Holy Spirit.

Every Mass begins in the same way.

And this is a profession of faith in the name, the one name, of these three divine persons,

of the triune God.

So we could say in a certain sense believing in the Trinity

is the very substance of being a Christian insofar as we are consecrated by baptism in this holy

and mysterious name. But to say that is not to answer the question, is it irrational to believe in the

Trinity? And it might seem so.

Some people might make a fairly straightforward argument, an objection that might go something

like this. How can something be both one and three at the same time? That's simply a contradiction.

That's not what the Christian faith is professing, and we'll get to that

in a few minutes. Others might add another objection. It might go something like this. The word

Trinity isn't found in the Bible. And so they imply that this belief is not a part of divine

revelation. They might even suggest that it's a doctrine made up later by the church or by human beings.

You'll even sometimes hear people say things like, the church didn't believe in the Trinity until, say, the Council of Nicaea in 325 AD,

which professed that the son is consubstantial with the father.

...