Surprisingly, the black “mustard grain” itself is exceedingly small. In Jesus’ day it was the tiniest of the seeds commonly sown in Israel. (Mark 4:31) It has a diameter of about one twentieth of an inch [1 mm], justifying its use as the smallest unit of measure in the Talmud.—Berakhot 31a.

Christ also used a stimulating illustration to highlight how far even a minute amount of faith will go, stating: “Truly I say to you, If you have faith the size of a mustard grain, . . . nothing will be impossible for you.”—Matthew 17:20; Luke 17:6.