“For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and spirit, of joints and marrow, and discerning the thoughts and intentions of the heart.”

Hebrews 4:12

Two-Edged Sword Etymology (from Wiktionary):

From the notion that if two sides of the same blade are sharp, it cuts both ways. The metaphor may have originated from the Arabic expression  “sayf ḏū ḥadayn”double-edged sword”. In the Bible, the word of God is described as a being sharper than a double-edged sword.

The metaphor is first attested to in English in the 15th century. It is not to be confused with a double-ended sword.