References to the Most Holy Trinity are to be found throughout the Jewish and then the newly Catholic Sacred Scriptures from Genesis to the Apocalypse. When I was a seminarian in the bad old days, as bad or worse than today, when heresy was everywhere to be found among seminary profs, any references to the Most Holy Trinity in any of the Scriptures was simply denied, as if this were something palatable to, I don’t know, Jews, maybe Muslims. Maybe it was just lust to deny anything that was a teaching of the Catholic Church just to do it. One was then “hip” and “groovy” and “up-to-date”, but really just a thief who was stealing the truth away from the children of God.
Let’s take a timely example of the Most Holy Trinity in the Scriptures. Right after Christmas we have the feast of Saint Stephen, Deacon, the First Martyr. Let’s take a look at the Lectionary entry for the first lesson (ACTS 6:8-10; 7:54-59).
Stephen, filled with grace and power, was working great wonders and signs among the people. Certain members of the so-called Synagogue of Freedmen, Cyrenians, and Alexandrians, and people from Cilicia and Asia, came forward and debated with Stephen, but they could not withstand the wisdom and the Spirit [the Holy Spirit: see “filled with the Holy Spirit” below] with which he spoke.
When they heard this, they were infuriated, and they ground their teeth at him. But he, filled with  the Holy Spirit, looked up intently to heaven and saw the glory of God and  Jesus standing at the right hand of  God [the Father], and he said, “Behold, I see the heavens opened and the Son of Man standing at the right hand of God.” But they cried out in a loud voice, covered their ears, and rushed upon him together. They threw him out of the city, and began to stone him. The witnesses laid down their cloaks at the feet of a young man named Saul. As they were stoning Stephen, he called out “Lord Jesus, receive my spirit.”
The Holy Spirit, inspiring the Sacred Scriptures, say that the Jews cannot withstand the Holy Spirit that filled Saint Stephen. They perceive the Holy Spirit even while Stephen speaks of Jesus and the Father.
Is the Holy Spirit being rude in pointing out “the Jews” like this? No. This is presented in the sense of even the Jews cannot withstand the Holy Spirit (so, much less us, the non-Jews). As the “young man named Saul” would later write as Saint Paul about the Jews:
“They are Israelites; theirs the adoption, the glory, the covenants, the giving of the law, the worship, and the promises; theirs the patriarchs, and from them, according to the flesh, is the Messiah. God, who is over all, be blessed forever. Amen.” (Romans 9:4-5).
We are all the Jews who attacked Stephen. But only the Jews have the promises and patriarchs. But we’ve all crucified the Son of the Living God with our sin. And we are all redeemed. To be saved, well, that involves the free will of us all.
Let’s be up-to-date not be rejecting the Triune God who is Truth and Love, but by being lifted up into the timelessness of He who created time and entered into time, drawing all to Himself across time, across Calvary, when He was lifted up on the Cross, He who born to die, whose birth we celebrate even as we honor the first martyr for Him.