Holy, holy, holy is the Lord.
We do not know what we will see in heaven. It's a mistery of faith. However, some holy people had special visions of God's dwelling. They even heard voices coming down to them. Afterwards they shared their experiences with other believers. Important is that they were passive during revelations and received the divine experience as a gift. They did perceive the flashes of lightning and flames which were the sings of God's presence. But as human beings they were not able to look on God himself. The reason was that God's majesty is too splendid and gorgeous to be comprehended by anyone. So every creature has to cover one's eyes and humbly praise the Creator saying: Holy, holy, holy is the Lord.