His Word.

Jeremiah 1:12, Amplified
Then said the Lord to me, You have seen well, for I am alert and active, watching over My word to perform it.

Isaiah 55:11, Amplified
So shall My word be that goes forth out of My mouth: it shall not return to Me void [without producing any effect, useless], but it shall accomplish that which I please and purpose, and it shall prosper in the thing for which I sent it.

Hebrews 4:12, Amplified
For the Word that God speaks is alive and full of power [making it active, operative, energizing, and effective]; it is sharper than any two-edged sword, penetrating to the dividing line of the breath of life (soul) and [the immortal] spirit, and of joints and marrow [of the deepest parts of our nature], exposing and sifting and analyzing and judging the very thoughts and purposes of the heart.

Psalm 18:30, Amplified
As for God, His way is perfect! The word of the Lord is tested and tried; He is a shield to all those who take refuge and put their trust in Him.

2 Samuel 22:31, Amplified
As for God, His way is perfect; the word of the Lord is tried. He is a Shield to all those who trust and take refuge in Him.