"...Praise the Lord, all ye Gentiles, and magnify Him, all ye people. And again, Isaias saith: There shall be a root of Jesse; and He that shall rise up to rule the Gentiles, in Him the Gentiles shall hope." (Romans 15: 11-13)

This reference will again arise for the third of the "O Antiphons", O Radix Jesse, O Root of Jesse, which antiphons are sung with the Magnificat during Vespers from December 17th to the 23rd:
O Root of Jesse, which standest for an ensign of the people, at Whom the kings shall shut their mouths, Whom the Gentiles shall seek, come to deliver us, do not tarry. | O Radix Jesse, qui stas in signum populorum, super quem continebunt reges os suum, quem Gentes deprecabuntur: veni ad liberandum nos, jam noli tardare. |
Who then is Jesse and how does this relate to Christ? Jesse was the father of King David, and the prophecy concerning the Messiah was that he would be of the house and lineage of David and be born in David’s city of Bethlehem. "And Thou, Bethlehem Ephrata, art a little one among the thousands of Juda: out of thee shall he come forth unto me that is to be the ruler in Israel: and his going forth is from the beginning, from the days of eternity." (Micah 5:2) The Tree of Jesse relates then to the genealogy of Jesus Christ in relation to the house of David and to the fulfillment of the messianic prophecies in Him.
Speaking of the words of Isaiah, Dom Gueranger had this to say in his Liturgical Year:
How much is contained in these magnificent words of the prophet! The branch; the flower that is to come from it; the Spirit which rests on this flower; the seven gifts of this Spirit; peace and confidence established on the earth; and, throughout the world, one brotherhood in the kingdom of the Messias! St. Jerome, whose words are read by the Church in the lessons of the second nocturn of this Sunday, says that the branch which cometh forth from the root of Jesse, is the blessed Virgin Mary, who had contact with no shrub or plant; and that the flower is the Lord Jesus, who says in the Canticle of canticles: `I am the flower of the field, and the lily of the valley.'
The Tree of Jesse is something we have often seen depicted within our sacred art. It shows Christ and the Virgin at the top of this tree (or in some instances, the Virgin holding the Christ-child) with Jesse reclining at the bottom and trunk proceeding forth from his side; proceeding upward to Christ are various Old Testament figures, including King David and often King Solomon.
While this imagery appears in various forms, from stained glass, manuscripts, icons, murals, to sculptured carvings, one of the most spectacular and grandiose depictions of this must surely be that from the 13th century, painted on the ceiling of Michaeliskirche in Hildesheim.


(Click to enlarge)