God's Word is powerful because all the omnipotence of the Godhead, Father, Son and Holy Spirit are active through the Word! The Trinity gives power to the Word!
A second source of power from God's Word is His Truth!
What is the power of God's Truth?
Obviously, God's Truth is powerful because it is the expression of His character. It shows you Who He is.
Life is without meaning or substance until you fully know Who He is and surrender to Him in faith.
It is also powerful because it shows you who you are!
The truth of God's Word convicts you of your sin and points you to your Savior. There is no other reliable source of exposing your sinful nature apart from the Holy Word of God.
God's Word reveals the truth of what you can become in Christ!
In Christ, through obedience to His Word, you can be sanctified or "set apart" unto God and made holy.
Studying and obeying the Word of God can keep you from being "of the world" while you are "in the world".
The Word is powerful because truth is powerful!