Adolf Schlatter (1852-1938), The History of the Christ, p. 298:
Jesus demanded from the disciples the renunciation of exhibition of their strength and assertion of their significance, not only in their dealings with God but also in their dealings with one another. . . . The self-admiration that considered one's own religious conduct to be superior and that enjoyed and exhibited it was considered by him to be sin in the case of his own followers just as in Judaism. . . . This rule had greatest significance for the disciples' common life, since a religious community acts differently depending on whether it exhibits its worship and admires its ethical achievements or whether it transfers the aim of its longing from itself to God and thus protects against self-admiration.
A lesson to be re-learned, over and over.