Why do people have visions?

There are various purposes. The vision Saul (Paul) had was for the purpose of converting him to true Christianity and making him into an apostle.

The visions of John, Ezekiel, Zechariah, Malachi, and Daniel were multi-purpose. Part of their visions were for our time, the time of the end, the end of the age of man's rule of this planet.

Some visions are for the purpose of showing what the future will be. These will increase as we get closer to the end.

In the last days God will pour out his Spirit on all flesh; our sons and daughters will prophesy; old men will dream dreams; young men will see visions (Joel 2:28, Acts 2:17).