According to the Old Testament, Yahweh/Jehovah regularly and violently made Himself manifest.
According to the New Testament, there were miraculous works performed to prove that the Messiah was who He said He was and that His followers were authentic.
Why are there no such public manifestations of Jehovah/Yahweh/Jesus/Holy Spirit today? I say public because some individuals describe very personal experiences detailing some sort of miracle or divine intervention in their lives, most often at a low or desperate point. I have no interest in discounting such personal experiences. But I must ask why are we not receiving the same benefit of public manifestations of divinity today?
Watchtower theology answers that times have changed and that all the "proof" we need today of divine activity is the modern-day "miracle" that is the visible organization of Jehovah's Witnesses.
Why have things changed?