... why cannot the other sacraments be had by desire? Confirmation by desire, Marriage by desire, Priesthood by desire.
Well, marriage can be confected by
votum. In fact, the
votum is the essential component there.
Nevertheless with the other two, Confirmation and Priesthood, the answer is apparent. These are the "character" Sacraments, where the Sacramental effect is inextricable from the character that's conferred. Baptism is also a character Sacrament, and there's an effect of the Sacrament that's missing in a BoD scenario. BoD reduces it to a triviality, a non-repeatability marker, and a badge of sorts that some people in Heaven have and others don't. But what does it actually DO? What EFFECT does it have? According to BoD theory, pretty much nothing.
But, no, the Church Fathers viewed the "seal" or the "crown" (their terms for the character) as essential to permit entry into the Kingdom, to become adopted children of God the Father, to gain entry into the Royal Family of the Holy Trinity. It's like Our Lord's Divine DNA, as it were, imprinted upon the human being to cause God to recognize the person as if he were His son, an adopted son, but a son nonetheless. Church Fathers taught that God became man to make men gods. This was no hyperbole. They meant it. When receiving the Sacrament of Baptism, we take on a divine character, the characteristics of God, God the Son, and become adopted family members of the Holy Trinity. Human nature also lacks the capacity to see God as He is, God's Face, as it were, the supernatural vision of God, and the character also endows the soul with this power or this capability or this faculty ... just as the Priesthood and Confirmation endow men with other types of powers and capabilities.
BoD theory guts the importance of the Sacramental character, and I'd be more amenable to BoD theory that held we receive the character of Baptism or, as Nishant came to accept, for those God wishes to save, He administers the Sacrament via His angels. It would take but a drop of water and a moment for the angels to confer the Sacrament of Baptism. Who can prove that God does not do this? In fact, this is what St. Cyprian thought was happening with BoB, that the angels pronounced the words (the form) and that blood could supply for water. Alternatively, the angels could bring some water as well. This is why St. Cyprian, the first to speak of BoB, called it the Sacrament. Later commentators, not understanding what he meant, wrongly concluded that this was an erroneous statement, unaware of what he thought was taking place in BoB, that it was not some replacement for the Sacrament, but an alternative mode of administering it.