Today, August 15th, is the Feast of the Assumption of the Blessed Virgin Mary.
The Assumption of Mary into Heaven, often shortened to the Assumption and also known as the Feast of Saint Mary the Virgin, or the the Falling Asleep of the Blessed Virgin Mary (the Dormition), according to the beliefs of the Catholic Church, Eastern Orthodoxy, Oriental Orthodoxy, and parts of Anglicanism, was the bodily taking up of the Virgin Mary into Heaven at the end of her earthly life.
The Catholic Church teaches as dogma that the Virgin Mary "having completed the course of her earthly life, was assumed body and soul into heavenly glory".
While there are many "Marian Hymns," there aren't many that deal specifically with the Assumption. This one, is not "Assumption specific," but is specifically linked with the Feast of the Presentation (February 2nd). It is a solid tune and text, and often used as a processional on Marian Feasts.
The melody is by Louis Bourgeois (c. 1510-1559), and the tune is known as "Mon Dieu, prete-moi l'orielle." It comes from the "French Psalter" of 1542. This harmonization is by Ralph Vaughan Williams (1872-1958).
The fine text is by Bishop Reginald Heber (21 April 1783 – 3 April 1826).
The score is attached below, as well as a photo of the famous painting of the Assumption by Peter Paul Rubens (1577-1640). Portraits of Rubens and Heber are attached, as well as a photo of Ralph Vaughan Williams.
The full text is given in the First Comment.