How do we know that there is only one doctrine in the Word of God?

The sermon reinforces that there is only one doctrine in the Word of God, and that is the doctrine of Christ, encapsulated in the message of His crucifixion and its significance for salvation. The preacher uses multiple scriptural references—such as 2 John 9 and 1 Timothy 1:3—to illustrate that different teachings (doctrines) stem from false teachings and that adherence to the doctrine of Christ is essential for knowing God. Any deviation or focus on other teachings diminishes the truth and leads to spiritual confusion.