Jesus Christ knew that he had the truth. He had been with God in heaven, and was taught directly by the heavenly Father. So he was sure that what he believed was right. But what about Jesus’ apostles?

After about three years of close association with his apostles, Jesus said in prayer to God: “The sayings that you gave me I have given to them, and they have received them and have certainly come to know that I came out as your representative.” The apostles knew that Jesus Christ had come from God. So they were sure of the way of salvation, for Jesus taught them the truth directly.​—John 17:8; 14:6.

Well, consider: How did Jesus’ apostles know they had the truth? It was because they had received the teachings that Jesus directly heard from Almighty God. And we today have those teachings faithfully preserved for us in the Bible! Jesus’ apostles and their companions wrote them down. But, of course, we cannot know the truth if we do not read what they wrote.