'A sickle,' as in Revelation 14, signifies the divine truth of the Word, because 'a harvest' signifies the state of the church regarding divine truth in its final state. So 'reaping,' which is done with a sickle, signifies ending the state of the church, and executing judgment. Because this is done by divine truth of the Word, this what 'a sickle' signifies.

(References: Apocalypse Revealed 643; Revelation 14:14, 14:15, 14:16, 14:17, 14:18, 14:19)