Sword of the Spirit

Also, accept the helmet of salvation, and the sword of the spirit, that is, God’s word.—Ephesians 6:17

Two-edge sword
Hebrews 4:12— For the word of God is alive and exerts power and is sharper than any two-edged sword and pierces even to the dividing of soul and spirit, and of joints from the marrow, and is able to discern thoughts and intentions of the heart.

Old Testament review
Judge Ehud, a Judge of Israel took the time to make a specific two-edge sword that served a purpose to carry out judgment against the King of Moab. (Judges 3:15, 16) Since God's word is likened to a two-edged sword, (Hebrews 4:12) Christians ought to take the time to study God's word and even prepare specific material with a purpose to carry out their ministry, using the "sword of the spirit". (Ephesians 6:17)

Judges 3:15, 16— [15] Then the Israelites called to Jehovah for help, so Jehovah raised up for them a savior, Ehud the son of Gera, a Benjaminite who was left-handed. In time the Israelites sent tribute through him to Eglon the king of Moab. [16] Meanwhile, Ehud made for himself a two-edged sword, a cubit long, and he strapped it underneath his garment on his right thigh.