Eph 6:10-12
"Finally, be strong in the Lord and in the strength of his might. Put on the whole armor of God, that you may be able to stand against the schemes of the devil. For we do not wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness, against the spiritual forces of evil in the heavenly places."
Spiritual warfare is real but invisible. The enemies are not people (sarx kai haima), but spiritual powers: rulers (archas), authorities (exousias), cosmic powers of darkness (kosmokratoras), spiritual forces (pneumatika tes ponerias). The armor is necessary because the enemy is real and powerful.
Eph 6:14-17
"Stand therefore, having fastened on the belt of truth, and having put on the breastplate of righteousness, and, as shoes for your feet, having put on the readiness given by the gospel of peace. In all circumstances take up the shield of faith... and the helmet of salvation, and the sword of the Spirit, which is the word of God."
The 6 pieces of the armor: (1) belt of truth — integrity; (2) breastplate of righteousness — the righteousness of Christ; (3) gospel shoes — readiness to proclaim; (4) shield of faith — extinguish flaming darts; (5) helmet of salvation — protection of the mind; (6) sword of the Spirit — the Word of God, the only offensive weapon.