The thing that was so startling about Jesus to his disciples is how much of his life and what he did paralleled things that were written in what Christians call the Old Testament.
Consider the story of Abraham about to sacrifice Isaac. How that relates to Jesus's sacrifice. Even the events are similar. Isaac riding in.a donkey, carrying wood up the hill, obedient to the end even though Isaac would have easily been able to escape the clutches of a man as old as Abraham.
Consider the story of Joseph, how he was loved by his father, betrayed by Judah for silver, ended up at the right hand of Pharaoh.
Consider the many psalms of David that describe the exact situation Jesus finds himself in.
Really though, you could write a whole book on the parallels and scriptures that unexpectedly found themselves in the life of Jesus, and these things were seen as proofs to the followers of Jesus. There are so many it is really startling. In fact, Jesus' entire life account can even be said to be a parable in itself. Not only did Jesus teach in parables, his life was a parable.
And sure, if you were to simply adopt an attitude of hard skepticism, you will find none of it convincing. At best, you could simply claim that all the accounts were written as a hodge podge of Old Testament scripture, that the whole thing is just a constructed story.
You know, if you want to play the hard skeptic.
But the apostolic church is still around today, somehow even surviving its first few centuries under persecution.. people even up until contemporary times being tortured to death before they apostate. In the last century, over 20 million martyred, mostly by governments who promoted socialism and saw religion as a great evil on the world perpetuated by the oppressors of the people. The same type of rhetoric you found in those places is used by atheists today, they literally use the same arguments that the soviets used. They orobably got tgem from the same place. When you go to the library or bookstore, nearly every writing on the subject of Christianity is subversive in some way.
Why do so many go to the grave, all this over what the skeptic can easily dismiss as silly fables and stories?
Because the faith teaches people to love The Truth above all else, to be temperate in all things, to esteem others higher than the self, and to love their fellows even unto death. Anyone who wishes to hinder or even eradicate such a faith is being guided by the worst kind of evil.
Such a pure faith should be encouraged, for the betterment of the entire world.