"Jesus answered, “I am the way, the truth, and the life. No one comes to the Father except through Me.
"Lord, show us the Father and that will be enough for us."
"Anyone who has seen me has seen the Father. How can you say, 'Show us the Father'?"
"Don't you believe that I am in the Father, and that the Father is in me? The words I say to you I do not speak on my own authority. Rather, it is the Father, living in me, who is doing his work."
...
No proof. All talk.
Last comment first: while you would never understand the gospel from just a few verses (though a few verses can sometimes tell us the most key things!), the idea there is 'no proof' is a familiar objection -- Christ Himself was directly challenged to give more proof, in person, face to face (even though He had healed the blind, the lame, those with leprosy, and even raised the dead). They didn't want to only hear that others they knew were testifying about miracles done, but wanted one on demand.
Cynically.
It seems, with a hostile attitude, like -- "Yeah?
Prove it."
In this passage, after
slandering Jesus in a major, horrific way in front of the people (just before this, above in the same chapter), next some come to Him and demand He prove Himself with a sign:
[Not long after vilely slandering Jesus they come to Him:]
38 Then some of the Pharisees and teachers of the law said to him, “Teacher, we want to see a sign from you.”
39 He answered, “A wicked and adulterous generation asks for a sign! But none will be given it except the sign of the prophet Jonah. 40 For as Jonah was three days and three nights in the belly of a huge fish, so the Son of Man will be three days and three nights in the heart of the earth. 41The men of Nineveh will stand up at the judgment with this generation and condemn it; for they repented at the preaching of Jonah, and now something greater than Jonah is here. 42 The Queen of the South will rise at the judgment with this generation and condemn it; for she came from the ends of the earth to listen to Solomon’s wisdom, and now something greater than Solomon is here."
Matthew 12 NIV
He quotes to them from their scriptures, and basically tells them: NO, you will get no sign but that which requires trust/faith (and it seems they will hear of this only 2nd hand later, that He rose from the dead, they will hear and have to choose whether to trust, without much help (unless they become humble we learn!)).
So, they said: PROVE IT.
And He responds: No, you get no proof.
They demanded. With a nasty, vile attitude. Not a loving or friendly way.
Imagine:
It's like as if someone comes to you hearing you can fix a major problem with their car or one of a friend, and instead of asking you in a friendly way or offering anything, or a normal way of asking, instead scoffs at you in a hostile way. Mocks you in a major way.
And also is arrogant, and clearly willing to pretend you didn't fix cars before, and in the future, you can see....
Would you then work to fix the car of the hostile person that is unfriendly and tries to make you look like a fake?
I would not. I'd tell them they are doing a wrong. If they
truly repented of the wrong, then I would help them.
That's actually the rules: if you repent of your wrongs to God, then He will help you.
And that even applied to those that had died without a chance to hear about Christ, we learn in 1rst Peter chapter 3 (v18-20) -- He went to the "spirits in prison", those dying without the gospel, where those dying in the Flood are the instance given, and makes proclamation to them. They get a chance, since they never heard before.