May one say that the elect in heaven will be invested, as it were, with a royal dignity?
Yes, because the beatific vision unites them to God, and thus they participate in the divinity of God; and since God is the immortal King of ages, the elect participate in this sovereign royalty and its glory (XCVI. 1).
Is it then by reason of this that the blessed are said to receive a crown in heaven?
Yes, it is for this precisely (XCVI. 1).
Next - The Catechism of the Summa - Tertia Pars - LIII. OF ETERNAL HAPPINESS (D)