A triptych is 3 separate pictures, placed together, in art.
Originally, this formed a folding screen which could travel with a rich person, and be set up on a flat service or altar, as a screen of inspiring images to pray in front of. The 3 separate panels also give scope to express different eras or people or people or settings.
So it might look like this:

Nowadays, when you come to a similar 3 piece framed opening, placed on a flat surface, it makes me think of the contemplation of the self, the mirror set on the dressing table.
Perhaps that is a coincidence – that it’s simply a stable structure and also lets you view your face from front and both sides at the same time. Who knows who invented this?
All that is by the by, the simple thing is that, today, as I looked at my Pinterest account, 3 images selected looked well together. There were surprising echoes of feel and tone. And so, I placed them together. I’d be interested to know your comments, and what you think of them.

On the left, Soapstone contemplative, pinned by artparks.co.uk
Middle: Sacred Space: Le Corbusier’s Saint-Pierre de Firminy Church, France (1971-) 2006
On the right, photo pinned by http://www.1924.us