In the ending, the priest's incessant talk about religion was just the sign of his craving for acceptance( perhaps all Catholics share this unpleasant feature). His sympathy for the dying man was condescending and his motive self-righteous. And I so understand the reason why Charles insisted on the absence of the priest by the deathbed of Lord Marchmain. It was the church that drove Sebastian away from him. And it was the church that he feared will part him and Julia, which it did. Lord Marchmain and Sebastian both tried to fight against or flee from religion, eventually both failed and yielded. The unfathomable power of it confused Charles(and me) and this confusion formed the very core of tragedy.
Anyway, the tragedy has been foretold. Religion has used the concept of sin to punish those who believed in it and those who didn't as well. True love though once glorious, had been shattered.