why did Jesus have to leave to send the holy ghost.?
He didn’t “have” to leave to send the Holy Spirit. That’s just the way God set it up.
You must remember, Jesus is coming back. It doesn’t say in the Bible when he comes back we are all going to loose the Holy Spirit that dwells within us.
Imagine that. We will have the Holy Spirit within us, and we will be looking at Jesus at the same time, and yet, the two are still God.