I recently typed up an answer here on the network, and made use of the phrase "Holy Trinity". I did so in an ironic, non-religious (and hopefully non-offensive!) context, knowing vaguely what the phrase means and where the phrase comes from.

However, I've never really figured out where that phrase comes from.

I very well now understand that this particular phrase never specifically occurs in the Bible; instead, it is used as shorthand to refer to "The Father, The Son, and The Holy Spirit" when discussing this[ese] [three] entity[ies] in scripture.

But, if this phrase was never in the Bible to begin with, how did it come about?

Note that I'm not particularly interested in a specific religious answer on this one, but simply the etymology of this phrase. If it did so happen to come out of a religious institution, I'd like to know which one.

I recently typed up an answer here on the network, and made use of the phrase "Holy Trinity". I did so in an ironic, non-religious (and hopefully non-offensive!) context, knowing vaguely what the phrase means and where the phrase comes from.

However, I've never really figured out where that phrase comes from.

I very well now understand that this particular phrase never specifically occurs in the Bible; instead, it is used as shorthand to refer to "The Father, The Son, and The Holy Spirit" when discussing this[ese] [three] entity[ies] in scripture.

But, if this phrase was never in the Bible to begin with, how did it come about?

Note that I'm not particularly interested in a specific religious answer on this one, but simply the etymology of this phrase. If it did so happen to come out of a religious institution, I'd like to know which one.