Romeo’s beloved has taken a vow of chastity, which “merits her bliss” and guarantees that she’ll go to heaven.  The unavailability of someone so beautiful and wise drives Romeo to despair.

But in the Christian worldview, despair is a grave sin because it implies that you don’t believe in God’s power to redeem. Perhaps Romeo is suggesting that while his beloved is going to heaven, he is destined for damnation because he has tied his hopes to the earthly world.