Actually, the correct understanding of Trent can be easily deduced by its Catechism, which is an AUTHENTIC and Authoritative interpreter of this Council, which nobody here is.
First, the section:
CHAPTER IV.
"A description is introduced of the Justification of the impious, and of the Manner thereof under the law of grace.
By which words, a description of the Justification of the impious is indicated,-as being a translation, from that state wherein man is born a child of the first Adam, to the state of grace, and of the adoption of the sons of God, through the second Adam, Jesus Christ, our Saviour. And this translation, since the promulgation of the Gospel, cannot be effected, without the laver of regeneration, or the desire thereof, as it is written; unless a man be born again of water and the Holy Ghost, he cannot enter into the Kingdom of God."
This is merely stating that the desire to receive baptism is a necessary disposition to receiving it. It is not directly related to baptism of desire.
Catechism of Trent, Section on Baptism:
Dispositions for Baptism
Intention
"The faithful are also to be instructed in the necessary dispositions for Baptism. In the first place they must desire and intend to receive it; for as in Baptism we all die to sin and resolve to live a new life, it is fit that it be administered to those only who receive it of their own free will and accord; it is to be forced upon none. Hence we learn from holy tradition that it has been the invariable practice to administer Baptism to no individual without previously asking him if he be willing to receive it. This disposition even infants are presumed to have, since the will of the Church, which promises for them, cannot be mistaken."
Faith
Besides a wish to be baptised, in order to obtain the grace of the Sacrament, faith is also necessary. Our Lord and Saviour has said: He that believes and is baptised shall be saved.
Clearly then one needs both the solemn intention to receive baptism in order to receive its grace, AND it needs to be coupled with faith in order to receive its grace.
SO it is not amazing that the council says what it does, it merely asserts the plain and the obvious: To be justified we need the grace of the sacrament. It (baptism) cannot be had without the necessary accompanying disposition: First, the desire to receive it, which implies faith.
If you read the council, it says that the justification cannot be effected WITHOUT baptism or the desire for it. They go together: Disposition and reception.
If a person is baptized without the will to receive baptism, the character on the soul is imprinted, but none of the graces take effect. Worse, if a person is baptized simply out of a desire to have fire insurance and without taking the sacrament seriously, it is a mortal sin of sacrilege. The waters that ought to save in this case actually condemn. If the person were to die after arising out of the baptismal font, blasphemously smug in having gotten his way, and he were killed on the spot, he would descend to Hell.