John Lightfoot on Matthew 13:32

[Which, indeed, is the least of all seeds, &c.] Hence it is passed into a common proverb, According to the quantity of a grain of mustard: and According to the quantity of a little drop of mustard, very frequently used by the Rabbins, when they would express the smallest thing, or the most diminutive quantity.

[Is the greatest among herbs.] "There was a stalk of mustard in Sichin, from which sprang out three boughs: of which, one was broke off, and covered the tent of a potter, and produced three cabes of mustard. R. Simeon Ben Chalaphta said, A stalk of mustard was in my field, into which I was wont to climb, as men are wont to climb into a fig-tree."