A spirit once latched onto me at my left, asking whether I knew how he could get into heaven. I was permitted to answer that being allowed into heaven was up to the Lord alone, since only he knows what we are like.
A large number of people coming from the world seek nothing more than to enter heaven, not having the least idea what heaven or heavenly joy is. They do not realize that heaven is the sharing of love, or that heavenly joy is the joy this love imparts. Those who do not know are first taught what heaven and its joy are, and one of the ways they learn is through personal experience.
For example, one spirit who himself had recently arrived from the world shared the same desire for heaven [as the first spirit]. To give him a sense of heaven’s nature, his inner recesses were opened up so that he could feel something of heavenly joy, but when he felt it, he started to wail and writhe, begging to be released. He was so distressed that survival was impossible, he said. As a result, his inner reaches were closed off to heaven and he then revived.
This demonstrates how anxiety and the gnawing of conscience torture people who are let in to heaven for just a short time, if they are not right for it.
from Secrets of Heaven, Volume 1, Section 537