The Holy Eucharist is the most powerful weapon to overcome the enemy.

Four weapons are required to overcome the enemies in unseen warfare which are: an unshakeable hope in God, resisting and struggling with sin, and prayer. However, the highest and most powerful and effective of all spiritual weapons is the holy sacrament of the Eucharist. The four weapons receive power from the forces and gifts of grace, obtained for us by the blood of Christ. But the sacrament of the Eucharist is Christ's blood itself, and His flesh itself, in which Christ is Himself present as God. When we use those four weapons, we fight the enemy with the power of Christ; in the latter case our Lord Christ Himself strikes down our enemies through us, or in company with us. For he who easts Christ's flesh and drinks His blood abides with Christ, and He in him, as He said: 'He that eateth my flesh, and drinketh my blood, dwelleth in Me, and I in him' (John vi.56). Therefore, when we overcome the enemies, it is the blood of Christ which overcomes, as it is written in Revelation: 'and they overcame him' (the slanderous devil) 'by the blood of the Lamb' (Rev. xii.11)

Unseen Warfare by St. Niodemus of the Holy Mountain, page 225