Who sings "Climb Ev'ry Mountain" in the film, "The Sound of Music"?

One of the top moments in the film "The Sound of Music" is the Reverend Mother singing “Climb Ev'ry Mountain,” to encourage Maria von Trapp after she returns from the Von Trapp estate. Julie Andrews playing Maria loves her role as governess, but she is still aspiring to be a nun. But instead of becoming a nun, she falls in love with Navy Captain Von Trapp and marries him. Maria then points out in the film that she aims to climb every mountain in her life.

It was reported in newspapers that Oscar Hammerstein II felt that the metaphors of climbing mountains and fording streams better fitted Maria's quest for her spiritual compass. The actual muse behind the song was Sister Gregory, the head of Drama at Rosary College in Illinois. She sent letters to Hammerstein and to Mary Martin, the first Maria von Trapp on Broadway. Her letters described the parallels between a nun's choice for a religious life and the choices that humans must make to find their purpose and direction in life. When she read "The Sound of Music" manuscript with its lyrics, she confessed that it "drove [her] to the Chapel" because the lyrics conveyed a "yearning that … ordinary souls feel but cannot never communicate."