How is Jacques' museum message resolved in Chapters 29-31?

Although the entire mystery isn't solved, in this section the mystery of Jacques' museum messages is, or, at least Langdon thinks it is. Sophie and Langdon find what Jacques wanted them to find, the gold key with the fleur-de-lis and the initials P.S. engraved in it. That indicates to Langdon that Jacques was a member of the Priory of Sion, which points Langdon and Sophie in the right direction, they hope.