A sword whose blade is sharpened on both sides is able to penetrate and cut at every contact point and with every movement. This means that it can be thrust more quickly and deeply and can cut more easily.

What does the Bible say about double-edged sword?

The word of God is quick, and powerful, and sharper than any two edged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart.

Why are double-edged swords bad?

In other words, the poetic implication of cutting both ways supersedes the historical reality of the actual weapon. "Double-edged sword", as a metaphor, has always been linked with "cuts both ways", meaning it can (figuratively) hurt both the person attacked and the attacker.