This is CS Lewis's so-called trilemma, from Mere Christianity (1952):
I am trying here to prevent anyone saying the really foolish thing that people often say about Him: "I'm ready to accept Jesus as a great moral teacher, but I don't accept his claim to be God." That is the one thing we must not say. A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic — on the level with the man who says he is a poached egg — or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God, or else a madman or something worse. You can shut him up for a fool, you can spit at him and kill him as a demon or you can fall at his feet and call him Lord and God, but let us not come with any patronizing nonsense about his being a great human teacher. He has not left that open to us. He did not intend to...
Insofar as anything brief is true, then I regard Lewis's argument as true.
Yet I read this when I was an atheist, it didn't have any significant impact on me - it didn't make me a Christian; and this presumably applies to most people who read it.
Why? Since the argument is short and easy to follow; why doesn't it convince?
The reason, I'm pretty sure, is that for the the trilemma to work requires several assumptions to be in place; and these assumptions are nowadays pretty generally denied.
The first is that, for Jesus to be God, God must be assumed to exist; which most people deny. Indeed, most people cannot regard God as a coherent or even meaningful concept. So, the trilemma fails.
Another assumption of the trilemma that is commonly denied is that the Bible is valid. Most people nowadays assume the Bible to be completely made-up fantasy, or maybe so garbled as to have become utterly unreliable - so anything in the Bible can and should be completely ignored.
This last denial is particularly devastating for Christianity. Two centuries of regarding the Bible as an historical document has led people to regard it as just that: and historical understanding is in a constant state of dispute and revision, participation is restricted to professionals, and therefore the Bible cannot be a basis for answering ultimate questions.
As I so often return to emphasising, these days; at root all our convictions rest upon intuition; and until people can attain and accept intuitive validation of God, the Bible, and Jesus; they are self-doomed to incoherence, nihilism and misery.