It named the builders.
It stated religious beliefs.
It defended his claim to rule.
The text contained the royal lineage, so it can't be any answer but the last one.
Since everything seem to be designed to bear witness to Pacal's right to rule, even his own sarcophagus, it is safe to assume that the text was meant to legitimate his right to rule, which brings us to It defended his claim to rule.
Thomas More, who died for what he believed in, coined the word (Utopia).