יואל ד:יג פירוש: רש״י

Stretch out a sickle etc.—Draw the swords, you who go on My mission to destroy the nations.

for the harvest is ripe—I.e, for their time has arrived, and he compared the matter to harvest, which is harvested with sickles when it becomes completely ripe.

come press for the winepress is full—of grapes. Come and tread them; i.e., the measure of their iniquity is full. press Heb. רְדוּ, an expression of pressing [or ruling]. Cf. (Gen. 1:28) “And rule (וּרְדוּ) over the fish of the sea.”