Soncino on Yeshayahu 41:14

Yisrael is again bidden, as in v10, not to fear and a new reason is added.  Not only is G-d his support, but Yisrael has an inherent spiritual strength and power of resistance to his enemies as the threshing-sledge to the corn.

worm - a symbol of weakness, meekness and humility.  The worm crawling upon the ground is at the mercy of every passer-by (cf. Tehillim 22:7).

redeemer - the Hebrew go'el is a technical term applied to the nearest relative whose duties included the redemption or buy back of the kinsman who sold himself, or his sold property or, if killed, the avenging of his blood by slaying the murderer.  It is possibly in this sense applied to G-d, the Redeemer and Avenger of His people Yisrael.