In 2 Kings 6:8-23, the Bible describes how God provides an army of angels leading horses and chariots of fire to protect the prophet Elisha and his servant, and opens the servant's eyes so he can see the angelic army surrounding them. Here's a summary of the story, with commentary:
Ancient Aram (now Syria) was at war with Israel, and the king of Aram was disturbed by the fact that the prophet Elisha was able to predict where Aram’s army was planning to go, and passed that information along to Israel’s king in warnings so the king could plan the Israeli army’s strategy. Aram’s king decided to send a large group of soldiers to the city of Dothan to capture Elisha so he wouldn’t be able to help Israel win the war against his nation.
Verses 14-15 describe what happens next: "Then he sent horses and chariots and a strong force there. They went by night and surrounded the city. When the servant of the man of God got up and went out early the next morning, an army with horses and chariots had surrounded the city. 'Oh no, my lord! What shall we do?' the servant asked.
Being surrounded by a large army with no way to escape terrified the servant, who at this point in the story could only see the earthly army that was there to capture Elisha.
The story continues in verses 16-17: "'Don’t be afraid,' the prophet answered. 'Those who are with us are more than those who are with them.' And Elisha prayed, 'Open his eyes, LORD, so that he may see.' Then the LORD opened the servant’s eyes, and he looked and saw the hills full of horses and chariots of fire all around Elisha.
Bible scholars believe that angels were in charge of the horses and chariots of fire that were present on the surrounding hills, ready to protect Elisha and his servant. Through Elisha's prayer, his servant gained the ability to see not just the physical dimension, but also the spiritual dimension. Then he could see the angelic army that God had sent to protect them.
Verses 18-19 then record: "As the enemy came down toward him, Elisha prayed to the LORD, 'Strike this army with blindness.' So he struck them with blindness, as Elisha had asked. Elisha told them, 'This is not the road and this is not the city. Follow me, and I will lead you to the man you are looking for.' And he led them to Samaria." Verse 20 describes Elisha praying for the soldiers' sight to be restored once they entered the city, and God answered that prayer, so they could finally see Elisha -- and also the king of Israel, who was there with him. Verses 21-23 describe Elisha and the king showing mercy to the army and holding a feast for the army to build a friendship between Israel and Aram. Then, verse 23 ends by saying, "the bands from Aram stopped raiding Israel’s territory."
In this passage, God responds to prayer by opening people's eyes both spiritually and physically -- in whatever ways are most useful for their growth.