Elijah had prayed that it not rain and it did not rain for 3 and a half years. Then the Lord wanted him to pray for rain and he told King Ahab that rain was on the way.

So Ahab went up to eat and drink. And Elijah went up to the top of Carmel; then he bowed down on the ground, and put his face between his knees, and said to his servant, “Go up now, look toward the sea.” So he went up and looked, and said, “There is nothing.” And seven times he said, “Go again.” Then it came to pass the seventh time, that he said, “There is a cloud, as small as a man’s hand, rising out of the sea!” So he said, “Go up, say to Ahab, ‘Prepare your chariot, and go down before the rain stops you’” (1Ki. 18.42–44). 

Knowing that God likes seven, we are not surprised that He had Elijah operate in this manner. It reminds us of Naaman dipping seven times in the water for the cleansing of his leprosy.