Mosaics designed by John Henry Rosen at St Matthew's Cathedral in Washington adorn the baptistery (1967-1968), the chapel of the Blessed Sacrament (1968-1970) and the tympanum above the main portal on the façade (1970), where "Christ blessing with the open book of the Gospel of St Matthew" was depicted. All the mosaics were made by The Ravenna Mosaic Company of Saint Louis, a company with which the artist collaborated on many occasions.

The Roman Catholic Cathedral of Washington (since 1939 the archdiocese) was built between 1893 and 1895, designed by the renowned New York architect Christopher Grant La Farge (1862-1938), of the New York architectural firm Heins & LaFarge. It was here that John F. Kennedy's funeral service was held in 1963.

The baptistery, located to the left of the church entrance, at the end of the portico added to the façade, was decorated with mosaics designed by John Henry Rosen in 1967-1968. They were consecrated on 28 July 1968 by the Revd John K. Cartwright, provost of the cathedral from 1948 to 1968 and commissioner of the designs. The mosaics decorate two walls of a quadrangle with chamfered corners, in a hexagonal plan. They were placed on adjacent (perpendicular to each other) walls, in recesses of different widths (one of which is twice as wide as the other). The mosaic opposite the entrance (on the west wall) depicts the baptism given by St Matthew to an Ethiopian, with the inscription: "and matthew was | baptizing and preaching | in ethiopia rom mart ix 21" ("And matthew was | baptizing and preaching | in ethiopia rom mart ix 21"), taken from the liturgical memory of St Matthew in the "Martyrologium romanum", falling on 21 October.

The larger of the scenes (on the north wall) depicts an angel moving the water of the pool of Bethesda , with the inscription: "tharsus, angel of the waters" ("Tarsus, angel of the waters"), whose actions are said to have given the water its healing properties, and a lame man who was healed thanks to the water of the pond (as evidenced by his discarded crutches) - an event described in the Gospel of St John (Jn 5:1-18). The essential content of the representation is described on the banner appearing at the top of the composition: "For an angel of the Lord used to come | at certain times into the pool | and the water was troubled | St John V 4" ("For an angel descended at certain times [into the pool] and then the water was troubled", Jn 5:4). Below, against a golden background, is another inscription - a hymn of thanksgiving in praise of God: "wherefore i bless thee o | creature of water | by the living god | by the true god | by the holy god" ("Therefore I bless thee, creature of water, by the living god, by the true god, by the holy god"). The composition is depicted against a plain gold background, with which the angel's red robes and the healed man's luscious green cloak contrast strongly. Rosen, traditionally, rendered the water in silver. The painting is signed at the bottom right, on the banderole: "john de rosen".

The mosaic that fills the altar wall of the Blessed Sacrament chapel, adjacent to the presbytery to the west, has similar formal features. The gold background shows the apostles at Emmaus, at the moment when they recognise Christ 'in the breaking of the bread' - as the inscription on the right informs us: 'they | recognized | him in the | breaking | of the | bread'. The figure of Christ breaking the bread itself is not present in the painting; this representation is replaced by the tabernacle placed on the small altar mensa, symbolically completing the depicted scene. In fact, the Apostles stand on either side of the tabernacle, facing it with faces and gestures. The painting is signed on the lower right: "john | de rosen". The chapel was consecrated on Palm Sunday, 22 March 1970, by Cardinal Patrick O'Boyle, then Archbishop of Washington. The completion of the mosaic in the chapel was delayed due to personnel changes in the position of rector of the cathedral. It was completed when the Rev John G. Kuhn became rector, who also commissioned the mosaic in the tympanum, above the entrance to the church (1970).