You won’t see it coming.
People believe the “Kingdom of God/Heaven” is a future thing because they look around and don’t see any evidence that it exists. There are no markings, no trails, no remains or residue to be found. So, the conclusion is that because it can’t be observed by standard measure, the Kingdom of God/Heaven must not be there.
That conclusion is just… well… crap.
See, the kingdom of God/Heaven is like a bat. Wait a minute - what?!
Yep, blind as a bat.
See, we all learn in grade school that, while bats have small, poorly developed eyes, they actually aren’t blind; in fact they can see pretty good. But, bats are nocturnal and those tiny eyes don’t do well at night and are useless for navigating through pitch-black caves and caverns. To compensate, bats use echolocation - the bounce sounds off of nearby objects to create “visual maps” which allow them to “see” in the dark.
What most of us don’t learn in grade school is that the sounds that bats emit are “ultrasonic” - sounds at such a high frequency that humans can’t hear them. And, that’s good ‘cause those sounds come out from the bats at whopping 140 decibels. If you go to a really loud rock concert you’re talking noise (yeah, I said noise) at about 115-120 decibels - right at the point of pain for normal, sober human beings. So basically, if we could hear the bat calls, they’d burst our eardrums!
There’s a whole world of sights and sounds and things we can’t see, hear, or otherwise perceive but nevertheless exist. The kingdom of God/Heaven is one of those things… and Jesus tells us so.
Luk 17:20-21 Once Jesus was asked by the Pharisees when the kingdom of God would come. He answered them, "The kingdom of God is not coming with a visible display. (21) People won't be saying, 'Look! Here it is!' or 'There it is!' because now the kingdom of God is among you."
You won’t see it coming.
Better still, you didn’t see it coming… it’s already here.