fortress - A fortified place; a large and permanent fortification, a stronghold; a place of defense or security
Psalm 91 says that if we make God our dwelling and rest in His shadow then we can say of the Lord that He is our refuge and fortress. It strikes me that there is some action involved on our side. We must willfully choose to put ourselves in that place of obedient and child-like faith so He can rescue and protect us.
And, the other thought that strikes me in this passage is how much you are either for Him or against Him. There is no middle-of-the-road Christianity that pleases Him. He desires to be our Lord, yet, so many mainstream denominations limit Him to being just their Savior. We are not to love Him with the watered down love of the world (yum...I just love that ice cream, love your new shoes, etc...). No, the love I believe He speaks of is a love that puts all of our own motives and agendas aside to contently follow where He leads. Even when it costs something.
Starting with verse 14 the Lord demonstrates what happens to those who love him:
Because he loves me," says the LORD, "I will rescue him;
I will protect him, for he acknowledges my name.
15 He will call upon me, and I will answer him;
I will be with him in trouble,
I will deliver him and honor him.
16 With long life will I satisfy him
and show him my salvation."