It goes with the notion that St. John put in his gospel account, “For God so loved the world that he gave up His only begotten Son, not to condemn the world, but that the world might be saved through Him.” Also, in Marks gospel, Jesus Himself says, “He who believes and is baptized will be saved, he who does not believe will be condemned.” Notice the omission of baptism in the condemnatory portion of the sentence. It doesn’t say, “he who does not get baptized will be condemned.”
Jesus wills salvation on everyone. He instituted the sacramental system for imparting His grace on they who receive Him. However, Jesus knows that not all who come to the full knowledge of the saving power of Christ will be in a position to be baptized before they die. Let’s say that one makes a perfect act of contrition and repentance while the hangman is slipping the noose over his neck. Do you think that the executioner will pause so that someone can dunk or splash the poor fellow with water before he snaps his neck? Probably not. however, if the act of repentance is sincere, do you not think that Jesus wills that he be saved from damnation? This is the essence of “Baptism of desire”. A perfect example is Jesus and the thief on the cross. He made a sincere act of repentance while hanging next to Jesus, and Jesus promised him a place in paradise. Did you hear Jesus commanding someone to baptize the thief before he died? God establsihes sacraments for us, but He is not bound by them. God is free to save whomever He pleases.
