Only because they trusted did they obey. Obedience is easily, clearly seen as expression of faith, but it is not the only expression of faith. It is the expression of faith that we have emphasized through the years. It is because of our emphasis that it is so familiar to us. But our emphasis and familiarity with obedience does not make it the only expression of faith.
Faith exists and expresses itself in many forms.
Like our believing that God will resurrect us to eternal life. Faith is trusting when you have done all that is in your power to do. Like David trusting God to protect him when he was fleeing from King Saul. Like our trusting God to sustain us when we must endure a horrible crisis. Faith is confidence when the solution does not lie within yourself.