The Sword of the Spirit, which is the word of God - The sword is the only offensive weapon in the collection of armour. In the passage, the soldier is displayed mainly as someone who is in a position of defence, as one who stands, in order to take his position and keep his ground. However, in order to be effective in battle, the sword is necessary for the soldier to injure or kill the enemy.
The preached Gospel, “the power of God” (Romans 1:16;1 Corinthians 1:18), is our offensive weapon provided by the Spirit and Bible for meeting the lunge of the assailant and beating him back. It is the spoken word of God from the mouth of a believer, backed up with a heart of faith, trust and confidence in God - that sets the enemy fleeing!
No armour is mentioned for protecting the back because at no point are we to surrender to the enemy by retreating!
The bible tells us to submit to God, resist the devil and he will flee from you - not to run away from him! (James 4:7)
We are to stand our ground and use the word of God by speaking/declaring His promises of love over our friends, family, career, circumstances, nation, etc.
Be bold! For His word will not return to Him void, but will accomplish the purpose for which it is sent (Isaiah 55:11). For He watches over His word to perform it (Jeremiah 1:12)
Therefore hold fast to your confession of hope without wavering, for He who promised is faithful! (Hebrews 10:23)
God is on YOUR side! Trust Him, today and always!