When Saul saw David go forth against the Philistine, he said to Abner, the captain of the host, Abner, whose son is this youth? Abner said, As your soul lives, O king, I can't tell.
In applying this story, I believe it is legitimate to see Goliath as representing the many enemies that frustrate individual believers as we seek to live for God. However, I believe primarily the application deals with defeating those enemies bent on defeating and destroying God’s people en masse. Contemporary movements designed to discredit God and remove Christianity from a land are what Goliath personifies.