I have written in the past about the different approaches to portraiture and sacred art in the Western naturalistic form of the baroque (in the article: Is Some Modern Sacred Art too Naturalistic?) . I this I discussed the fact that many examples of sacred art are painted as though they are portraits and end up looking like a staged tableau in which the boy or girl nextdoor is dressed up in old fashioned clothing. Consider the work of someone I met when I was studying the academic method in Florence, Matthew James Collins. I know of know one else who knows more about the art of the baroque and High Renaissance periods. Matt is an American who still lives and works in Italy. His portfolio is here (look at his sculpture and landscapes of the Italian countryside too)
I was looking at this portfolio a few days ago and several paintings of faces caught my eye. First this portrait left. It has all the right elements: it is painted in some areas loosely, and in some with more detail and tighter control, but always with precision. The variation in focus and colour content reflect the Christian understanding of the human person: those areas that we look at most, especially the eyes and the mouth, and which reveal emotion and thought and aspects of the soul, are those we look at the most when we look at someone. These are the parts that contain the most detail and the most natural colouring.
If you look at the right side of the face, the part that in this portrait is more distant than the other. To make this read properly, the artist must make everything on this side of the face slightly smaller than the left; and the right edge must be blurred enough to give a sense of a turning edge, but still sharp enough to retain the right sense of contrast with the background. This is terrifically difficult to get right - even Titian and Rembrandt (for the most part absolute Masters) got it wrong occasionally. In this portrait Matt has captured it. Notice how even the glint on each eye varies to reflect the slight perspective - the right eye is more distant and the glint is smaller and less bright. These tiny specks of white can make or break a portrait.
Part of the essence of the baroque style is a strong emphasis on tonal description and the reduction of natural colour in all but the main focal points of the painting. Even if you master this, which is hard enough, then there is very often a problem in that the shadow areas look flat and dull. Matt has introduced some energy into the shadow by using a different of colours in any one area that are, broadly speaking, tonally equivalent (ie if you took a black and white photo there would be very little contrast) but of slightly different colours. This gives life and variety to the composition.
Notice also how he varies the background tone in order to enhance local contrast, so next to some dark edges of the head the background is slightly lighter and the opposite for light edges. However, he does so while avoiding a distracting, exaggerated patchiness and maintaining a unified impression.
It is an exceptional portrait, in my opinion. But the focus on the individual that we see here and is necessary in portraits would not be appropriate for sacred art. And this is the difficulty for many artists today who are trained primarily as portrait painters.
Contrast it with the first head study shown below. All the essentials elements are here too and handled just as well. However, this is not a portrait. It is one of a series of studies that Matt is doing to develop his skill in allegorical or explicitly sacred art. Matt has deliberately chosen to lessen the portrait elements of the face. This is the same device used by the baroque masters of the 17th century to paint the faces of saints. It causes to focus less on the individual, and more on those general characteristics that are common to all of us but are exemplified in an exceptional way in saints. Again this is difficult to do: it is a question of a shift of emphasis, rather than featuring one aspect to the exclusion of the other). Think of any of the paintings of St Francis of Assisi by the Spanish baroque painter Zurburan. The psychological aspects are communicated through posture and gesture as much as facial expressions but if this is overdone, the result is sentimentality, or even melodrama. This emphasis on the general can be seen, for example, one of the most famous pieces of sacred art produced in the 17th century, by Velazquez. The face of Christ is in shadow and is clearly very different from a portrait (I have put a detail of the face from this painting at the bottom.)
The reason that I bring this to your notice is that here we have an artist is unusual in that he understands this subtle distinction between the two styles.
Matt does not have a large portfolio of sacred art to point to at the moment. He is a working artist with a young family portraiture and landscape are his staples. He mentioned to me ruefully, that even when people do commission sacred art, they want the 19th century style and so most of his sacred art has more of this negative aspect than he would choose to paint if he was not painting for sale.
Works shown below, first: head study; third: Christ Carrying the Cross; fourth: The Triumph of Hermes. All are by Matthew James Collins. The final images are of the crucifixion by Velazquez.