Throughout the Psalms, David refers to God as his fortress, refuge, and strength. He faced many physical and spiritual battles throughout his life and saw firsthand how God provides a strong fortress regardless of what attacks us. In the ancient world the fortress was often walled off from the rest of the city, supplied with food, water, and ammunition where the people could be protected, and the city could be defended. David knew that he did not need to fear, because in God he found a fortress stronger than any attack this world could muster.
We all have our own fortresses that we run to when we face overwhelming circumstances. These fortresses can take the shape of people or relationships. They can also be material things in our lives that we think will bring happiness and take our minds off of our problems. Like David, we should realize that the one true fortress we have is with the one true God. This fortress will always protect and never let down.