"Has God forgotten to be merciful? Has he in anger withheld his compassion? Then I thought, 'To this will I appeal: the years of the right hand of the Most High." I will remember the deeds of the LORD; Yes, I will remember your miracles of long ago."
Despite a whole list of doubts David has in verses 7-9, David ultimately has one source of comfort: that God never changes. David reflects on God's track record, on how he has proven himself time and time again to be the God who performs miracles. And of course, we see that it is the Exodus account that gives David cause for faith.
Even though things look bad now, David trusts God never changes and in so doing knows what God will do. The only surprise with God is in how he does something, not if he does something, but when he acts you can be sure it will be mighty.
God is the only thing in this world which never changes, a solid rock and firm foundation we can hold onto. It is this trust in God's unchangeable character that forms the backbone of our faith.
Without great doubt, there cannot be great faith. The more doubts you have, the more we must rely on the truth of God, in his unchanging character. But don't just take my word for it, God's actions speak for himself. Everything rests on the belief that God is who he has revealed himself to be.