take the helmet of salvation: Just like a helmet protects a soldier’s head, the assurance of salvation protects a believer’s mind. It reminds believers that God has saved them and given them eternal life through faith in Christ.
the sword of the Spirit: This is the word of God. It is like a weapon believers use to answer attacks, either by sharing the good news about Jesus, or by speaking or remembering what God has said in Scripture (compare Jeremiah 23:29; Hebrews 4:12). A sword is a weapon with a long, sharp blade used in battle.