Just after he delivered the Parable of the Sower (Mark4:1-2, 35) while in a boat near Capernaum, Jesus told his disciples to launch out and go to the other side of the lake (Luke 8:22). The lake is the Sea of Galilee, which is in the shape of a spear from north to south with a decided bulge on the west side. Capernaum is situated on the northwest end of the lake near the River Jordan, which flows through the lake from the north and out its southern coast. The lake is about 140 feet deep at its deepest point and approximately 700 feet below sea level, making it the lowest fresh water lake on earth, second overall only the Dead Sea which the Jordan River empties into. The Sea of Galilee is about 8 miles across at its widest point and about 13 miles long. Jesus’ voyage from Capernaum to Gerasenes was about seven to eight miles on a southeast diagonal.
When Jesus told them to go to the other side of the lake, the disciples started for the other side, and not long afterward Jesus fell asleep in the rear of the boat (Luke 8:22-23). The Sea of Galilee “…is surrounded by table lands beyond which the great mountains rise. The rivers have cut deep ravines through the table lands down into the sea. These ravines act like great funnels to draw down the cold winds from the mountains; and thus the storms arise.” One such storm arose, while the disciples rowed across the lake on that day. It was a particularly violent storm, and even seasoned fishermen like Peter, Andrew, James and John feared for their lives.
The disciples went to Jesus, woke him from his sleep and told him they were in danger of sinking (Luke 8:24). Mark tells us they asked Jesus if he cared that they were about to perish (Mark 4:38), which may indicate Jesus’ first response upon awakening was that they weren’t in any real danger. In any event, Jesus arose and rebuked the sea and the winds, and there was a great calm.
Jesus then turned to the disciples and asked: “Where is your faith?” This reply begs the question: what did Jesus expect the disciples to trust in? Did he expect the disciples to trust in God to make their safety certain? Probably not, since God does not save all of his people from every natural disaster. So, at least sometimes, God permits some of his people to perish in accidents. Therefore, Jesus must have expected the disciples to trust in him. That is, Jesus told them to cross to the other side, and, when they woke him to tell him about the danger they were in, he may have indicated everything would be okay. Nevertheless, they questioned Jesus concern for them and his appreciation of the circumstance (Mark 4:38). Therefore, Jesus rebuked the winds and the waves, and turned to his disciples and asked: “Where is your faith?” In other words hearing is not enough. They should have believed in him and continued in their efforts to get to the other side. This is the only logical explanation I see for his question that fits the context. As for the disciples, they were astonished, wondering what manner of man Jesus was, because even the winds and the sea obey him (Luke 8:25). At first they were overwhelmed with their circumstance, and afterward they were overwhelmed with Jesus’ presence.
On a previous occasion (Luke 5:1-11) Jesus was in a boat with Peter and Andrew. He told Peter to launch out into the deep and lower the nets for a catch. The text there implies that Peter obeyed the Lord out of respect, but he didn’t believe they would catch anything. Therefore, he lowered a single net. To his surprise the net was full to the point of breaking, and when he and the others emptied the net into the boats (he had called for his partners to help), both were brought to the point of sinking. Peter was utterly astonished.
In both Scriptures a miracle took place, showing Jesus’ authority over nature. In both instances the boats were brought to the point of sinking, and both times the text shows the disciples were astonished.
In Luke 5:4-6 the disciples at least attempted to do as Jesus commanded them. Whether out of politeness or out of simple faith, they took measures to do as he said. However, in Luke 8:22-24 the disciples began by obeying Jesus in launching out toward the other side of the lake, but they stopped after the storm had arrived. In other words, they no longer attempted to get to the other side of the lake. Instead, they felt they had to take measures to fight the storm and broke off doing as Jesus told them. It may even be implied in Mark 4:38 that Jesus told them the storm wouldn’t hurt them, but they didn’t believe him.
Considering the two different events about Jesus and his disciples on the lake, it may be that Jesus wanted to show his disciples his authority over nature (Psalm 89:8-9; 93:3-4; 107:25-29), that it was the same as the authority of God. The leap to believing that Jesus is God in the flesh would have been great, considering the worldview of the Jews, but these events pave the way to such a consideration.
 William Barkley, commenting on Luke 8:22-25.