It strikes me as I read through Psalm 42 — as I often do — how crucial memory is to the process of faith in the midst of difficulty or depression. "These things I remember..." the psalmist says in verse 4. When God allows affliction, it is important to remember his historic faithfulness.

There is a reason the Israelites filled the ark of the covenant with mementos of God's faithfulness, and it's not because they were magic talismans.

When you are stuck, deep, despondent, or in despair, think back to what God has delivered you from in difficult times past. Remember how he has never really failed you. Remember your way all the way back to Mount Calvary and the empty tomb. Remembering God's historic faithfulness is the first step in enjoying his present faithfulness to you, even if you don't feel it.
"We are simple people. You can't remember ten things at once. Invariably, if you could remember just one true thing in the moment of trial, you'd be different. Bible 'verses' aren't magic. But God's words are revelations of God from God for our redemption.
"When you actually remember God, you do not sin. The only way we ever sin is by suppressing God, by forgetting, by tuning out his voice, switching channels, and listening to other voices. When you actually remember, you actually change. In fact, remembering is the first change."

– David Powlison, Making All Things New

You shall bind them as a sign on your hand, and they shall be as frontlets between your eyes.
– Deuteronomy 6:8

http://thegospelcoalition.org/blogs/gospeldrivenchurch/2013/09/03/remembering-is-the-first-change/