And he shall be like a tree planted by the rivers of water, that bringeth forth his fruit in his season; his leaf also shall not wither; and whatsoever he doeth shall prosper. Psalms 1:3
"The leaves shall not wither." He is saying this, that every word which flows forth out of your mouth in faith and love shall be a means to bring conversion and hope to many.
(Ehrman, Bart D., The New Testament and Other Early Christian Writings, Oxford University Press, New York, 1998, “The Letter of Barnabas”, chapter 11:8c, pg 353)