It is difficult for us to believe there is an invisible world, because we live in the natural world. We relate to what we can see, what we can hear, and what we can reach out and touch. But the Bible teaches there is a supernatural world, an invisible world. It is the realm of God and Satan, of angels and demons, and it is all around us. If we could somehow peek into the invisible world, it would blow our minds to see the angels of God at work, the demons of Hell at work, and all the spiritual activity swirling around us at any given moment.
The Bible gives an account of this actually happening to someone—the servant of Elisha the prophet. The servant woke up one morning to find the city surrounded by enemy forces. Panicked, he woke up Elisha, asking, "What shall we do?" (2 Kings 6:15).
Elisha, probably wiping the sleep from his eyes, told him, "Do not fear, for those who are with us are more than those who are with them" (verse 16). Then Elisha prayed, "Lord, . . . open his eyes that he may see." And the Bible tells us his servant looked up and saw "the mountain was full of horses and chariots of fire all around Elisha" (verse 17). Those were the angelic forces of God.
The activity of angels, especially in the lives of believers, is constant. We may not necessarily be aware of the presence of angels and can't necessarily predict how and when they will appear, but the Bible tells us they are there. Psalm 34:7 says, "The angel of the Lord encamps all around those who fear Him, and delivers them."
There is indeed a God, a Satan, angels, and demons. There is indeed an invisible world.