Isa 43:10 Ye are my witnesses, saith the LORD, and my servant whom I have chosen: that ye may know and believe me, and understand that I am he: before me there was no God formed, neither shall there be after me.

Now the skeptic chimes in:

You said God spoke to me, but I don't hear his voice.

You said that the Son testified, but I don't get it.

You said the Holy Spirit makes it make sense, but it's still gibberish.

And you say that Jesus testified in the flesh, but I wasn't there.

So how am I supposed to know?

Typically the answer is: You just have to believe, then you will know. I don't buy that answer either! Sometimes the answer is: Look at all the miracles! But the miracles werre not intended to persuade non-believers. Not even Jesus's teaching was intended to do that. ^[1]

1. ↑ Mt 13:15 For this people’s heart is waxed gross, and [their] ears are dull of hearing, and their eyes they have closed; lest at any time they should see with [their] eyes, and hear with [their] ears, and should understand with [their] heart, and should be converted, and I should heal them.