The painting is the The Foundation Mass of the Order of Trinitarians
painted by Juan Carreno de Miranda (Avila, 1614-Madrid, 1685). [Click here to see the full painting] "In the twelfth century, while celebrating Mass, Saint John
of Matha had a vision of an angel, with arms intersecting, resting its
hands on the heads of two captives. Following this vision he founded
the Order of the Most Holy Trinity, known as the Order of the
Trinitarians, dedicated to freeing Christian slaves from captivity
under the Muslims. This monumental canvas, commissioned for one of the
order's convents in Pamplona, is a masterpiece of the baroque style in its compositional flow." (Louvre Museum).