This argument will assume that you’re familiar with Jesus, and that you think He does have a supremely good moral character. If you do not believe this, then I suggest you carefully read the Gospels, study and think about them, and come to your own conclusion. This is more intended as an explanation of why I believe, rather than an argument to convince someone else, based on what I see in Jesus.
And what I see is, as I say, a supremely good moral character. In defiance of all custom and authority of the day, He did what was right. And not only did He do what was right, He explained and taught others, He had insights into the moral good that have never since been replicated. The greatest moral figures throughout history, those with the highest levels of moral reasoning, those who we have all looked up to, have looked up to Jesus. Even they recognise it.
Decades ago, Lawrence Kohlberg made some very interesting discoveries about the moral development of children and adults. To summarize (here’s some more detail), what we find is that people develop their moral reasoning ability in distinct, qualitatively different stages. It’s reasonably easy to recognise one stage from another, people always go through them one after the other and never skip, and rarely regress. People at higher stages can understand the reasoning of the stages below them (though they are distasteful of that reasoning), they feel drawn to and recognise higher stages, but importantly cannot imitate those higher stages. If you have a stage 4 person pretending to be stage 5, and a stage 5 person, and you question them and challenge them enough, the stage 5 person will remain consistent while the stage 4 person will eventually break down and admit (or demonstrate, if they’re stubborn) a lack of understanding.
So while none of us are at a stage of moral reasoning high enough to properly fully understand Jesus, we can recognise the supremacy of His moral character. The person of Jesus has a true moral character that cannot be faked, He really is that good. He is questioned and challenged enough in the Gospels to verify it to me, He really is supremely virtuous.
And so if He is that virtuous, I trust Him. Jesus alludes to this kind of reasoning in John 14:11, where He tells the disciples to trust what He says because He’s the one saying it. And then He says “or at least believe on the evidence of the works themselves.”. Jesus believes that His character should actually be more convincing than His miracles. Miracles can be faked, but moral character cannot.
The fact that this moral character cannot be faked also means that Jesus cannot be an invention. An author cannot convincingly write a character wiser than they are, they’d have to be that wise themselves. They might be able to provide one or two deepities, but if the character is challenged enough in their story, their “wisdom” will be exposed. Similarly, no author (let alone 4 authors in the case of the Gospels) could write a character at a higher moral stage than they themselves are at.
Now it’s relatively easy to write a character who behaves more morally than we do. I might write a character who gave money to the homeless person that I callously walked past, that’s not hard. We all recognise our own moral failures, and could create someone without them. What can’t be faked is the actual moral reasoning, the explanations and arguments for why we ought to do what we ought to do. Read more of Kohlberg to understand properly what I mean here.
And so if Jesus was an invention of an author, then it must be the case that the author was at the same level of moral reasoning that Jesus was at. And so we should trust them when they tell us that Jesus was a real person who did all of these things.
There are some objections here. Someone might say that Jesus was a real, virtuous person, but that later authors added the claims of divinity to the story. However if you look at Jesus’ moral system, you can see that these claims are central and integrative to the entire system, which would be incoherent without them. They can’t have been added without the system itself being added.
And now we are at the conclusion: Jesus has a supremely virtuous character that compels us to trust Him, and so when He tells us that He is the incarnate Son of God who died for our sins, and that we must repent of our sins, trust in His name, and obey God, we are compelled to believe Him. Because as the officer says in John 7:46: No-one ever spoke like this man.