For as only one thing is necessary, and as the theme of the talk is the willing of only one thing: hence the consciousness before God of one's eternal responsibility to be an individual is that one thing necessary.
Soren Kierkegaard, Purity of Heart is to Will One Thing, 1847 p. 197-198 - Upbuilding Discourses in Various Spirits (1847) - Purity of Heart (1847)