1st John 5: 9-10
1 John 5: 9-10 “We accept man's testimony, but God's testimony is greater because it is the testimony of God, which he has given about his Son. Anyone who believes in the Son of God has this testimony in his heart. Anyone who does not believe God has made him out to be a liar, because he has not believed the testimony God has given about his Son.”
In the book of Deuteronomy the people were told a single witness wasn’t enough in their justice system. (Deuteronomy 19:15) So here are three witnesses and divine witnesses at that!
John in the Gospel of John lists many more witnesses to Jesus. John the Baptist was a witness, Jesus’ deeds witnessed for Him, the scriptures witnessed to Him. Plus the Father and the Spirit. If we refuse to accept all of this, John says we call God a liar.
And notice where it says “he who believes in the Son of God” There’s a big difference between believing in a man and just believing a man. To believe someone is just believing a particular something he’s said to be true. To believe in someone is to believe everything they say is true and to accept the whole man as someone you would be willing to stand up for.